You could somehow make it so that if you try to do a tree feller on the tree that it only breaks the block that you use it on. Like somehow having the tree be unconnected to all parts of itself, but still have it be whole. Also, maybe have some really big trees that have a hollow inside, so that you could have a ladder or vines going down underground or up to a treehouse or something like that. Also, would you use Nbz to buy the custom trees or something else? Would you be able to choose what kind of custom tree you want that's avalible, or just get a random one?