diff --git a/Lecture/P06.GraphicalData/GraphicalData.UnitTest/GraphicalData.UnitTest.csproj b/Lecture/P06.GraphicalData/GraphicalData.UnitTest/GraphicalData.UnitTest.csproj
index fb168802..3f7d7ee6 100644
--- a/Lecture/P06.GraphicalData/GraphicalData.UnitTest/GraphicalData.UnitTest.csproj
+++ b/Lecture/P06.GraphicalData/GraphicalData.UnitTest/GraphicalData.UnitTest.csproj
@@ -6,9 +6,9 @@
     <ProjectGuid>{32EE831B-AD46-48AC-B303-23A6D818B8D5}</ProjectGuid>
     <OutputType>Library</OutputType>
     <AppDesignerFolder>Properties</AppDesignerFolder>
-    <RootNamespace>TP.MVVMExample.UnitTest</RootNamespace>
-    <AssemblyName>TP.MVVMExample.UnitTest</AssemblyName>
-    <TargetFrameworkVersion>v4.6.1</TargetFrameworkVersion>
+    <RootNamespace>TP.GraphicalData</RootNamespace>
+    <AssemblyName>TP.GraphicalData.UnitTest</AssemblyName>
+    <TargetFrameworkVersion>v4.7.1</TargetFrameworkVersion>
     <FileAlignment>512</FileAlignment>
     <ProjectTypeGuids>{3AC096D0-A1C2-E12C-1390-A8335801FDAB};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
     <VisualStudioVersion Condition="'$(VisualStudioVersion)' == ''">10.0</VisualStudioVersion>
@@ -16,6 +16,7 @@
     <ReferencePath>$(ProgramFiles)\Common Files\microsoft shared\VSTT\$(VisualStudioVersion)\UITestExtensionPackages</ReferencePath>
     <IsCodedUITest>False</IsCodedUITest>
     <TestProjectType>UnitTest</TestProjectType>
+    <TargetFrameworkProfile />
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
     <DebugSymbols>true</DebugSymbols>
diff --git a/Lecture/P06.GraphicalData/GraphicalData.UnitTest/MainViewModelUnitTest.cs b/Lecture/P06.GraphicalData/GraphicalData.UnitTest/MainViewModelUnitTest.cs
index 71283674..42cb8a42 100644
--- a/Lecture/P06.GraphicalData/GraphicalData.UnitTest/MainViewModelUnitTest.cs
+++ b/Lecture/P06.GraphicalData/GraphicalData.UnitTest/MainViewModelUnitTest.cs
@@ -2,10 +2,10 @@
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using System;
 using System.Windows;
-using TP.MVVMExample.Model;
-using TP.MVVMExample.ViewModel;
+using TP.GraphicalData.Model;
+using TP.GraphicalData.ViewModel;
 
-namespace TP.MVVMExample.UnitTest
+namespace TP.GraphicalData
 {
   [TestClass]
   public class MainViewModelUnitTest
diff --git a/Lecture/P06.GraphicalData/GraphicalData/App.xaml b/Lecture/P06.GraphicalData/GraphicalData/App.xaml
index aecb185c..35cf37da 100644
--- a/Lecture/P06.GraphicalData/GraphicalData/App.xaml
+++ b/Lecture/P06.GraphicalData/GraphicalData/App.xaml
@@ -1,4 +1,4 @@
-<Application x:Class="TP.MVVMExample.App"
+<Application x:Class="TP.GraphicalData.App"
              xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
              xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
              StartupUri="MainWindow.xaml">
diff --git a/Lecture/P06.GraphicalData/GraphicalData/App.xaml.cs b/Lecture/P06.GraphicalData/GraphicalData/App.xaml.cs
index 3c02b45d..7fdf377a 100644
--- a/Lecture/P06.GraphicalData/GraphicalData/App.xaml.cs
+++ b/Lecture/P06.GraphicalData/GraphicalData/App.xaml.cs
@@ -1,17 +1,17 @@
-using System;
-using System.Collections.Generic;
-using System.Configuration;
-using System.Data;
-using System.Linq;
-using System.Threading.Tasks;
+//____________________________________________________________________________
+//
+//  Copyright (C) 2018, Mariusz Postol LODZ POLAND.
+//
+//  To be in touch join the community at GITTER: https://gitter.im/mpostol/TP
+//____________________________________________________________________________
+
 using System.Windows;
 
-namespace TP.MVVMExample
+namespace TP.GraphicalData
 {
-    /// <summary>
-    /// Interaction logic for App.xaml
-    /// </summary>
-    public partial class App : Application
-    {
-    }
+  /// <summary>
+  /// Interaction logic for App.xaml
+  /// </summary>
+  public partial class App : Application { }
+
 }
diff --git a/Lecture/P06.GraphicalData/GraphicalData/GraphicalData.csproj b/Lecture/P06.GraphicalData/GraphicalData/GraphicalData.csproj
index ccd5c63f..5cbf18fd 100644
--- a/Lecture/P06.GraphicalData/GraphicalData/GraphicalData.csproj
+++ b/Lecture/P06.GraphicalData/GraphicalData/GraphicalData.csproj
@@ -58,16 +58,15 @@
       <SubType>Designer</SubType>
     </ApplicationDefinition>
     <Compile Include="DelegateExample.cs" />
-    <Compile Include="Model\DataLayerSimulator.cs" />
+    <Compile Include="Model\DataLayerr.cs" />
     <Compile Include="MVVMLight\RelayCommand.cs" />
     <Compile Include="MVVMLight\ViewModelBase.cs" />
     <Compile Include="Model\User.cs" />
-    <Compile Include="TreeViewExample\DelegateCommand.cs" />
-    <Compile Include="TreeViewExample\ITreeViewItem.cs" />
-    <Compile Include="TreeViewExample\MainWindow.xaml.cs">
+    <Compile Include="TreeView\MainWindow.xaml.cs">
       <DependentUpon>MainWindow.xaml</DependentUpon>
     </Compile>
-    <Compile Include="TreeViewExample\MyViewModel.cs" />
+    <Compile Include="TreeView\MyViewModel.cs" />
+    <Compile Include="TreeView\TreeViewItem.cs" />
     <Compile Include="ViewModel\MainViewModel.cs" />
     <Page Include="MainWindow.xaml">
       <Generator>MSBuild:Compile</Generator>
@@ -81,7 +80,7 @@
       <DependentUpon>MainWindow.xaml</DependentUpon>
       <SubType>Code</SubType>
     </Compile>
-    <Page Include="TreeViewExample\MainWindow.xaml">
+    <Page Include="TreeView\MainWindow.xaml">
       <Generator>MSBuild:Compile</Generator>
       <SubType>Designer</SubType>
     </Page>
diff --git a/Lecture/P06.GraphicalData/GraphicalData/MVVMLight/RelayCommand.cs b/Lecture/P06.GraphicalData/GraphicalData/MVVMLight/RelayCommand.cs
index 7bf929e8..291a6f53 100644
--- a/Lecture/P06.GraphicalData/GraphicalData/MVVMLight/RelayCommand.cs
+++ b/Lecture/P06.GraphicalData/GraphicalData/MVVMLight/RelayCommand.cs
@@ -1,8 +1,14 @@
-
+//____________________________________________________________________________
+//
+//  Copyright (C) 2018, Mariusz Postol LODZ POLAND.
+//
+//  To be in touch join the community at GITTER: https://gitter.im/mpostol/TP
+//____________________________________________________________________________
+
 using System;
 using System.Windows.Input;
 
-namespace TP.MVVMExample.MVVMLight
+namespace TP.GraphicalData.MVVMLight
 {
 
   /// <summary>
@@ -12,7 +18,7 @@ namespace TP.MVVMExample.MVVMLight
   /// Execute and CanExecute callback methods.
   /// </summary>
   /// <remarks>The <see cref="CommandManager"/>handles automatic enabling/disabling of controls based on the CanExecute delegate.</remarks>
-  internal class RelayCommand : ICommand
+  public class RelayCommand : ICommand
   {
 
     #region constructors
diff --git a/Lecture/P06.GraphicalData/GraphicalData/MVVMLight/ViewModelBase.cs b/Lecture/P06.GraphicalData/GraphicalData/MVVMLight/ViewModelBase.cs
index aa422e42..8ead58ff 100644
--- a/Lecture/P06.GraphicalData/GraphicalData/MVVMLight/ViewModelBase.cs
+++ b/Lecture/P06.GraphicalData/GraphicalData/MVVMLight/ViewModelBase.cs
@@ -1,11 +1,19 @@
 
+///____________________________________________________________________________
+//
+//  Copyright (C) 2018, Mariusz Postol LODZ POLAND.
+//
+//  To be in touch join the community at GITTER: https://gitter.im/mpostol/TP
+//____________________________________________________________________________
+
 using System.ComponentModel;
 using System.Runtime.CompilerServices;
 
 namespace TP.MVVMExample.MVVMLight
 {
-  internal class ViewModelBase : INotifyPropertyChanged
+  public class ViewModelBase : INotifyPropertyChanged
   {
+
     #region INotifyPropertyChanged
     public event PropertyChangedEventHandler PropertyChanged;
     #endregion
diff --git a/Lecture/P06.GraphicalData/GraphicalData/MainWindow.xaml b/Lecture/P06.GraphicalData/GraphicalData/MainWindow.xaml
index c5093337..cdc8fc4b 100644
--- a/Lecture/P06.GraphicalData/GraphicalData/MainWindow.xaml
+++ b/Lecture/P06.GraphicalData/GraphicalData/MainWindow.xaml
@@ -1,10 +1,9 @@
-<Window x:Class="TP.MVVMExample.MainWindow"
+<Window x:Class="TP.GraphicalData.MainWindow"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
-        xmlns:local="clr-namespace:TP.MVVMExample"
-        xmlns:vm="clr-namespace:TP.MVVMExample.ViewModel"
+        xmlns:vm="clr-namespace:TP.GraphicalData.ViewModel"
         mc:Ignorable="d"
         Title="MainWindow" Height="350" Width="Auto">
   <Window.Resources>
diff --git a/Lecture/P06.GraphicalData/GraphicalData/MainWindow.xaml.cs b/Lecture/P06.GraphicalData/GraphicalData/MainWindow.xaml.cs
index b41fe3be..aef369bd 100644
--- a/Lecture/P06.GraphicalData/GraphicalData/MainWindow.xaml.cs
+++ b/Lecture/P06.GraphicalData/GraphicalData/MainWindow.xaml.cs
@@ -1,24 +1,11 @@
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Text;
-using System.Threading.Tasks;
-using System.Windows;
-using System.Windows.Controls;
-using System.Windows.Data;
-using System.Windows.Documents;
-using System.Windows.Input;
-using System.Windows.Media;
-using System.Windows.Media.Imaging;
-using System.Windows.Navigation;
-using System.Windows.Shapes;
+using System.Windows;
 
-namespace TP.MVVMExample
+namespace TP.GraphicalData
 {
-    /// <summary>
-    /// Interaction logic for MainWindow.xaml
-    /// </summary>
-    public partial class MainWindow : Window
+  /// <summary>
+  /// Interaction logic for MainWindow.xaml
+  /// </summary>
+  public partial class MainWindow : Window
     {
         public MainWindow()
         {
diff --git a/Lecture/P06.GraphicalData/GraphicalData/Model/DataLayerSimulator.cs b/Lecture/P06.GraphicalData/GraphicalData/Model/DataLayerr.cs
similarity index 76%
rename from Lecture/P06.GraphicalData/GraphicalData/Model/DataLayerSimulator.cs
rename to Lecture/P06.GraphicalData/GraphicalData/Model/DataLayerr.cs
index 89ec9a9f..a52f1f16 100644
--- a/Lecture/P06.GraphicalData/GraphicalData/Model/DataLayerSimulator.cs
+++ b/Lecture/P06.GraphicalData/GraphicalData/Model/DataLayerr.cs
@@ -1,11 +1,11 @@
 
 using System.Collections.Generic;
 
-namespace TP.MVVMExample.Model
+namespace TP.GraphicalData.Model
 {
-  internal class DataLayer
+  public class DataLayer
   {
-    internal IEnumerable<User> User
+    public IEnumerable<User> User
     {
       get
       {
diff --git a/Lecture/P06.GraphicalData/GraphicalData/Model/User.cs b/Lecture/P06.GraphicalData/GraphicalData/Model/User.cs
index 454c2be2..3ff4e1ee 100644
--- a/Lecture/P06.GraphicalData/GraphicalData/Model/User.cs
+++ b/Lecture/P06.GraphicalData/GraphicalData/Model/User.cs
@@ -1,7 +1,7 @@
 
 using System;
 
-namespace TP.MVVMExample.Model
+namespace TP.GraphicalData.Model
 {
   /// <summary>
   /// Class User - a class representing user
diff --git a/Lecture/P06.GraphicalData/GraphicalData/Properties/AssemblyInfo.cs b/Lecture/P06.GraphicalData/GraphicalData/Properties/AssemblyInfo.cs
index 86f9e751..5166466c 100644
--- a/Lecture/P06.GraphicalData/GraphicalData/Properties/AssemblyInfo.cs
+++ b/Lecture/P06.GraphicalData/GraphicalData/Properties/AssemblyInfo.cs
@@ -1,11 +1,7 @@
 using System.Reflection;
-using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 using System.Windows;
 
-// General Information about an assembly is controlled through the following 
-// set of attributes. Change these attribute values to modify the information
-// associated with an assembly.
 [assembly: AssemblyTitle("WpfApplication2")]
 [assembly: AssemblyDescription("")]
 [assembly: AssemblyConfiguration("")]
@@ -14,22 +10,7 @@
 [assembly: AssemblyCopyright("Copyright ©  2016")]
 [assembly: AssemblyTrademark("")]
 [assembly: AssemblyCulture("")]
-
-// Setting ComVisible to false makes the types in this assembly not visible 
-// to COM components.  If you need to access a type in this assembly from 
-// COM, set the ComVisible attribute to true on that type.
 [assembly: ComVisible(false)]
-
-//In order to begin building localizable applications, set 
-//<UICulture>CultureYouAreCodingWith</UICulture> in your .csproj file
-//inside a <PropertyGroup>.  For example, if you are using US english
-//in your source files, set the <UICulture> to en-US.  Then uncomment
-//the NeutralResourceLanguage attribute below.  Update the "en-US" in
-//the line below to match the UICulture setting in the project file.
-
-//[assembly: NeutralResourcesLanguage("en-US", UltimateResourceFallbackLocation.Satellite)]
-
-
 [assembly: ThemeInfo(
     ResourceDictionaryLocation.None, //where theme specific resource dictionaries are located
                                      //(used if a resource is not found in the page, 
@@ -38,19 +19,7 @@
                                               //(used if a resource is not found in the page, 
                                               // app, or any theme specific resource dictionaries)
 )]
-
-
-// Version information for an assembly consists of the following four values:
-//
-//      Major Version
-//      Minor Version 
-//      Build Number
-//      Revision
-//
-// You can specify all the values or you can default the Build and Revision Numbers 
-// by using the '*' as shown below:
-// [assembly: AssemblyVersion("1.0.*")]
 [assembly: AssemblyVersion("1.0.0.0")]
 [assembly: AssemblyFileVersion("1.0.0.0")]
-[assembly: InternalsVisibleToAttribute("TP.MVVMExample.UnitTest")]
+//[assembly: InternalsVisibleToAttribute("TP.MVVMExample.UnitTest")]
 
diff --git a/Lecture/P06.GraphicalData/GraphicalData/TreeViewExample/DelegateCommand.cs b/Lecture/P06.GraphicalData/GraphicalData/TreeView/DelegateCommand.cs
similarity index 93%
rename from Lecture/P06.GraphicalData/GraphicalData/TreeViewExample/DelegateCommand.cs
rename to Lecture/P06.GraphicalData/GraphicalData/TreeView/DelegateCommand.cs
index 044c8595..40671ee3 100644
--- a/Lecture/P06.GraphicalData/GraphicalData/TreeViewExample/DelegateCommand.cs
+++ b/Lecture/P06.GraphicalData/GraphicalData/TreeView/DelegateCommand.cs
@@ -2,7 +2,7 @@
 using System;
 using System.Windows.Input;
 
-namespace TP.Lecture.TreeViewExample
+namespace TP.GraphicalData
 {
   /// <summary>
   /// Class DelegateCommand implements 
diff --git a/Lecture/P06.GraphicalData/GraphicalData/TreeViewExample/MainWindow.xaml b/Lecture/P06.GraphicalData/GraphicalData/TreeView/MainWindow.xaml
similarity index 90%
rename from Lecture/P06.GraphicalData/GraphicalData/TreeViewExample/MainWindow.xaml
rename to Lecture/P06.GraphicalData/GraphicalData/TreeView/MainWindow.xaml
index 5f1f7815..2608a1fd 100644
--- a/Lecture/P06.GraphicalData/GraphicalData/TreeViewExample/MainWindow.xaml
+++ b/Lecture/P06.GraphicalData/GraphicalData/TreeView/MainWindow.xaml
@@ -1,11 +1,10 @@
-<Window x:Class="TP.Lecture.TreeViewExample.MainWindow"
+<Window x:Class="TP.GraphicalData.TreeView.MainWindow"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
-        xmlns:local="clr-namespace:TP.Lecture.TreeViewExample"
         mc:Ignorable="d"
-        Title="Aplikacja" Height="350" Width="525">
+        Title="Application title" Height="350" Width="525">
   <Grid>
     <TreeView Name="TreeView" Margin="312,19,8,23" RenderTransformOrigin="0.5,0.5" ItemsSource="{Binding  HierarchicalAreas}">
       <TreeView.ItemTemplate>
diff --git a/Lecture/P06.GraphicalData/GraphicalData/TreeViewExample/MainWindow.xaml.cs b/Lecture/P06.GraphicalData/GraphicalData/TreeView/MainWindow.xaml.cs
similarity index 88%
rename from Lecture/P06.GraphicalData/GraphicalData/TreeViewExample/MainWindow.xaml.cs
rename to Lecture/P06.GraphicalData/GraphicalData/TreeView/MainWindow.xaml.cs
index 7480a977..78f08a46 100644
--- a/Lecture/P06.GraphicalData/GraphicalData/TreeViewExample/MainWindow.xaml.cs
+++ b/Lecture/P06.GraphicalData/GraphicalData/TreeView/MainWindow.xaml.cs
@@ -1,6 +1,6 @@
 using System.Windows;
 
-namespace TP.Lecture.TreeViewExample
+namespace TP.GraphicalData.TreeView
 {
   /// <summary>
   /// Interaction logic for MainWindow.xaml
diff --git a/Lecture/P06.GraphicalData/GraphicalData/TreeViewExample/MyViewModel.cs b/Lecture/P06.GraphicalData/GraphicalData/TreeView/MyViewModel.cs
similarity index 57%
rename from Lecture/P06.GraphicalData/GraphicalData/TreeViewExample/MyViewModel.cs
rename to Lecture/P06.GraphicalData/GraphicalData/TreeView/MyViewModel.cs
index 779f4567..20020f95 100644
--- a/Lecture/P06.GraphicalData/GraphicalData/TreeViewExample/MyViewModel.cs
+++ b/Lecture/P06.GraphicalData/GraphicalData/TreeView/MyViewModel.cs
@@ -1,10 +1,18 @@
-using Microsoft.Win32;
+//____________________________________________________________________________
+//
+//  Copyright (C) 2018, Mariusz Postol LODZ POLAND.
+//
+//  To be in touch join the community at GITTER: https://gitter.im/mpostol/TP
+//____________________________________________________________________________
+
+using Microsoft.Win32;
 using System.Collections.ObjectModel;
 using System.ComponentModel;
 using System.Windows;
 using System.Windows.Input;
+using TP.GraphicalData.MVVMLight;
 
-namespace TP.Lecture.TreeViewExample
+namespace TP.GraphicalData.TreeView
 {
   /// <summary>
   /// Class MyViewModel - ViewModel implementation 
@@ -12,30 +20,20 @@ namespace TP.Lecture.TreeViewExample
   /// <seealso cref="System.ComponentModel.INotifyPropertyChanged" />
   public class MyViewModel : INotifyPropertyChanged
   {
+    
     #region constructors
     public MyViewModel()
     {
-      HierarchicalAreas = new ObservableCollection<ITreeViewItem>();
-      Click_Button = new DelegateCommand(LoadDLL);
-      Click_Browse = new DelegateCommand(Browse);
+      HierarchicalAreas = new ObservableCollection<TreeViewItem>();
+      Click_Button = new RelayCommand(LoadDLL);
+      Click_Browse = new RelayCommand(Browse);
     }
     #endregion
 
     #region DataContext
-    public ObservableCollection<ITreeViewItem> HierarchicalAreas { get; set; }
-    public string PathVariable
-    {
-      get { return pathVariable; }
-      set { pathVariable = value; }
-    }
-    public Visibility ChangeControlVisibility
-    {
-      get { return _visibility; }
-      set
-      {
-        _visibility = value;
-      }
-    }
+    public ObservableCollection<TreeViewItem> HierarchicalAreas { get; set; }
+    public string PathVariable { get; set; }
+    public Visibility ChangeControlVisibility { get; set; } = Visibility.Hidden;
     public ICommand Click_Browse { get; }
     public ICommand Click_Button { get; }
     #endregion
@@ -49,16 +47,14 @@ private void RaisePropertyChanged(string propertyName_)
     #endregion
 
     #region private
-    private string pathVariable;
-    private Visibility _visibility = Visibility.Hidden;
     private void LoadDLL()
     {
-      if (pathVariable.Substring(pathVariable.Length - 4) == ".dll")
+      if (PathVariable.Substring(PathVariable.Length - 4) == ".dll")
         TreeViewLoaded();
     }
     private void TreeViewLoaded()
     {
-      ITreeViewItem rootItem = new ITreeViewItem { Name = pathVariable.Substring(pathVariable.LastIndexOf('\\') + 1) };
+      TreeViewItem rootItem = new TreeViewItem { Name = PathVariable.Substring(PathVariable.LastIndexOf('\\') + 1) };
       HierarchicalAreas.Add(rootItem);
     }
     private void Browse()
@@ -67,13 +63,11 @@ private void Browse()
       test.Filter = "Dynamic Library File(*.dll)| *.dll";
       test.ShowDialog();
       if (test.FileName.Length == 0)
-      {
         MessageBox.Show("No files selected");
-      }
       else
       {
-        pathVariable = test.FileName;
-        _visibility = Visibility.Visible;
+        PathVariable = test.FileName;
+        ChangeControlVisibility = Visibility.Visible;
         RaisePropertyChanged("ChangeControlVisibility");
         RaisePropertyChanged("PathVariable");
       }
diff --git a/Lecture/P06.GraphicalData/GraphicalData/TreeView/TreeViewItem.cs b/Lecture/P06.GraphicalData/GraphicalData/TreeView/TreeViewItem.cs
new file mode 100644
index 00000000..75dfc1fb
--- /dev/null
+++ b/Lecture/P06.GraphicalData/GraphicalData/TreeView/TreeViewItem.cs
@@ -0,0 +1,48 @@
+//____________________________________________________________________________
+//
+//  Copyright (C) 2018, Mariusz Postol LODZ POLAND.
+//
+//  To be in touch join the community at GITTER: https://gitter.im/mpostol/TP
+//____________________________________________________________________________
+
+using System;
+using System.Collections.ObjectModel;
+
+namespace TP.GraphicalData.TreeView
+{
+  public class TreeViewItem
+  {
+    public TreeViewItem()
+    {
+      Children = new ObservableCollection<TreeViewItem>();
+      Children.Add(null);
+      this.m_WasBuilt = false;
+    }
+    public string Name { get; set; }
+    public ObservableCollection<TreeViewItem> Children { get; set; }
+    public bool IsExpanded
+    {
+      get { return m_IsExpanded; }
+      set
+      {
+        m_IsExpanded = value;
+        if (m_WasBuilt)
+          return;
+        Children.Clear();
+        BuildMyself();
+        m_WasBuilt = true;
+      }
+    }
+
+    private bool m_WasBuilt;
+    private bool m_IsExpanded;
+    private void BuildMyself()
+    {
+      Random random = new Random();
+      for (int i = 0; i < random.Next(7); i++)
+        this.Children.Add(new TreeViewItem() { Name = "sample" + i });
+    }
+
+  }
+}
+
diff --git a/Lecture/P06.GraphicalData/GraphicalData/TreeViewExample/ITreeViewItem.cs b/Lecture/P06.GraphicalData/GraphicalData/TreeViewExample/ITreeViewItem.cs
deleted file mode 100644
index a660eae2..00000000
--- a/Lecture/P06.GraphicalData/GraphicalData/TreeViewExample/ITreeViewItem.cs
+++ /dev/null
@@ -1,42 +0,0 @@
-
-using System;
-using System.Collections.ObjectModel;
-
-namespace TP.Lecture.TreeViewExample
-{
-  public class ITreeViewItem
-  {
-    public ITreeViewItem()
-    {
-      Children = new ObservableCollection<ITreeViewItem>();
-      Children.Add(null);
-      this._wasBuilt = false;
-    }
-    public string Name { get; set; }
-    public ObservableCollection<ITreeViewItem> Children { get; set; }
-    public bool IsExpanded
-    {
-      get { return _isExpanded; }
-      set
-      {
-        _isExpanded = value;
-        if (_wasBuilt)
-          return;
-        Children.Clear();
-        buildMyself();
-        _wasBuilt = true;
-      }
-    }
-
-    private bool _wasBuilt;
-    private bool _isExpanded;
-    private void buildMyself()
-    {
-      Random random = new Random();
-      for (int i = 0; i < random.Next(7); i++)
-        this.Children.Add(new ITreeViewItem() { Name = "sample" + i });
-    }
-
-  }
-}
-
diff --git a/Lecture/P06.GraphicalData/GraphicalData/ViewModel/MainViewModel.cs b/Lecture/P06.GraphicalData/GraphicalData/ViewModel/MainViewModel.cs
index a426c7f9..c4ba48a0 100644
--- a/Lecture/P06.GraphicalData/GraphicalData/ViewModel/MainViewModel.cs
+++ b/Lecture/P06.GraphicalData/GraphicalData/ViewModel/MainViewModel.cs
@@ -1,16 +1,23 @@
+//____________________________________________________________________________
+//
+//  Copyright (C) 2018, Mariusz Postol LODZ POLAND.
+//
+//  To be in touch join the community at GITTER: https://gitter.im/mpostol/TP
+//____________________________________________________________________________
 
 using System;
 using System.Collections.ObjectModel;
 using System.Windows;
-using TP.MVVMExample.Model;
+using TP.GraphicalData.Model;
+using TP.GraphicalData.MVVMLight;
 using TP.MVVMExample.MVVMLight;
 
-namespace TP.MVVMExample.ViewModel
+namespace TP.GraphicalData.ViewModel
 {
   /// <summary>
   /// This class contains properties that the <see cref="MainWindow"/> can data bind to.
   /// </summary>
-  internal class MainViewModel : ViewModelBase
+  public class MainViewModel : ViewModelBase
   {
 
     #region constructors
@@ -68,7 +75,7 @@ public RelayCommand DisplayTextCommand
     public RelayCommand FetchDataCommend
     {
       get; private set;
-    } 
+    }
     #endregion
 
     #region Unit test instrumentation
@@ -80,8 +87,8 @@ public RelayCommand FetchDataCommend
     /// using <see cref="System.Runtime.CompilerServices.InternalsVisibleToAttribute"/>.
     /// </remarks>
     /// <value>The message box show delegate.</value>
-    internal Func<string, string, MessageBoxButton, MessageBoxImage, MessageBoxResult> MessageBoxShowDelegate { get; set; } = MessageBox.Show;
-    internal DataLayer DataLayer
+    public Func<string, string, MessageBoxButton, MessageBoxImage, MessageBoxResult> MessageBoxShowDelegate { get; set; } = MessageBox.Show;
+    public DataLayer DataLayer
     {
       get { return m_DataLayer; }
       set