Representing undo/redo history as a tree is quite different from representing the code structure as a tree. On the one hand I'm surprised no one seems to care that a response has nothing to do with the question... on the other hand, these AI tooling threads are always full of people talking right past each other and being very excited about it, so I guess it fits.
They certainly can be quite different things and in all current systems I know of the two are unrelated, but in my system they are one and the same.
That's possible because the source of truth for the IDE's state is an immutable concrete syntax tree. It can be immutable without ruining our costs because it has btree amortization built into it. So basically you can always
construct a new tree with some changes by reusing most of the nodes from an old tree. A version history would simply be a stack of these tree references.
