odoo widget for many2one field, provide a tree to select value, like the following screenshot.
This is based on jstree, and include jstree in the source code for easy deploying.
The related model must have parent_id and child_ids field, or you can use options to speficy corresponding field name.
For example:
parent_id = fields.Many2one('YOUR STRING', 'Parent')
child_ids = fields.One2many('YOUR MODEL', 'parent_id', string="YOUR STRING")
Than in the form view, set widget='many2one_tree'. Like this:
<field name="location_id" widget="many2one_tree"/>
In some situlation, One may want middle node can't be selected, you can achieve this by set middle_node_select to false for this field. Like this:
<field name="location_id" widget="many2one_tree" options="{'middle_node_select': False}"/>
There are other available options, only set them if you need;
child_ids- speficy similary field to child_ids.parent_id- speficy similary field to parent_id.