The reason for the esp is specifically to allow additional tree and bush placements. If you don't want or don't mind forgoing the additional placements and just want to replace the stock trees and bushes as placed in the original game, use the pure replacer method (no esp needed).
I like the idea of climbable trees, although being able to do so if the tree is a static should require a bit more effort than just walking into the model, like having to jump up into the lower branches or using a one-second levitate. The activator idea is good too, but I'd like the option to be able to physically climb a tree as well.
[edit] forgot an important word in that first bit.