i dont totally undarstand but i think you want more trees right?
The easier way is to DL WEU (world editor unlimited), here you can use unlimited trees, my advice is that you dont anything else with it(only trees), because some sh*t can happen to your map if you use WEU.
And one thing, when you open map once with WEU and save it in it, you wont be able to open the map with normal WE.