worldedit brush tool, voxel sniper, use the 1.2 pre-releases, or make tall trees using the dirt ring glitch. simply make rings of dirt starting and 4 blocks above a sapling and then make them at intervals of every 3 blocks as high as you want, and then grow the sapling and itll grow through pretty much all of the blocks. its hard to do sometimes, but releases very good results when it works