Mindmap with multiple roots

[oktomus]

Looking at Other Examples, we can see that it's possible to create a mermaid code with multiple graphs inside that are not connected together:

graph TB
    sq[Square shape] --> ci((Circle shape))

    subgraph A
        od>Odd shape]-- Two line<br/>edge comment --> ro
        di{Diamond with <br/> line break} -.-> ro(Rounded<br>square<br>shape)
        di==>ro2(Rounded square shape)
    end

    %% Notice that no text in shape are added here instead that is appended further down
    e --> od3>Really long text with linebreak<br>in an Odd shape]

    %% Comments after double percent signs
    e((Inner / circle<br>and some odd <br>special characters)) --> f(,.?!+-*ز)

    cyr[Cyrillic]-->cyr2((Circle shape Начало));

     classDef green fill:#9f6,stroke:#333,stroke-width:2px;
     classDef orange fill:#f96,stroke:#333,stroke-width:4px;
     class sq,e green
     class di orange

But with mindmaps, it's not possible. The code bellow generates the error message There can be only one root.

mindmap
  root((Part A))
    Origins
      Long history
      ::icon(fa fa-book)
      Popularisation
        British popular psychology author Tony Buzan
    Research
      On effectiveness<br/>and features
      On Automatic creation
        Uses
            Creative techniques
            Strategic planning
            Argument mapping
  root((Part B)
    Tools
      Pen and paper
      Mermaid

Is it possible to have multiple graphs in a mindmap? I would like to use mindmaps instead of graph to have a circular connection instead of a hierarchical vertical or horizontal one.

[Piratepie]

I'm pretty sure subgraphs are specific to flowcharts as that's the only place they're documented.