It depends on which trees you get,who made them and what you do after you build your game.
I can tell you that Sinistar's trees will work immediately and most of the other trees will too if after you build your game you place the textures into the same folder that your trees are in.
So let's say you build a game called Done.You would copy the tree textures and paste them into the Doneentitybanktree folder.
I know that Candles' trees work because I tested his tree pack.
I am checking some of the others now.
Oh,the trees have to be dynamic entities.