Did you see the tree view widget: https://appstore.home.mendix.com/link/app/112707/Mendix/Tree-View ?
That might be able to do what you want.
Regards,
Ronald
You can create a Menu document in your app that works just like the standard app-level navigation menu (with a separate set of menu options). In your page layout, you can use the Menu Bar (horizontal top bar) and Navigation Tree (vertical sidebar) widgets to render menus.