It's not that no one uses it, it's just that people tend not to right manuals for ActiveX controls.
However, your best shot at getting a list of methods and properties is to do this:
1. On the userform toolbox, right click and choose "Additional Controls"
2. Add the Treeview control (you will now have inadvertently added a reference to "Microsoft Windows Common Controls 6.0")
3. Press F2
4. On the dropdown that says "<All Libraries>" select "MSComctlLib"
5. In the box below this, type in "treeview"
6. A list of events, methods and properties for the class "Treeview" will then be presented.
7. It's up to you to mess about with them to work out what you need.
HTH