Selecting value from tree-view for managed metadata via PowerApps edit form for SharePoint list.

As you can see in that video, there are lots of possibilities, but a classic treeview is tricky/ugly to do I am afraid...  closest I got was to take the output of the choices() function which will bring back your term set into a collection and groupby() to then format the collection appropriately before then using a gallery/sub gallery technique.

Unfortunately that only works to 2 levels deep. 

I never took the time to find a pattern that can make it look like the classic tree-view of term sets :-(