@steve.page This isn’t how Anvil works. On the client side, there is a Python implementation written in javascript called skulpt. It covers most (but not all) of the standard library so you can write Python code and it will run in the browser.
However, there is no mechanism for you or anyone else to install third party Python libraries and use them. That’s only possible on the server side.
You’re correct that there is currently no tree-like component in the anvil toolbox. If you want one, your best bet is probably to investigate the plethora of javascript libraries available and incorporate one of those into your app.