Minecraft wiki entry for Tree_farming, associated text: Wait a day (or use bone meal), then harvest the trees and get the saplings. Place the chest nearby to store the saplings (and axe, if players have one) in there. Then, you can extend the grid if you like, as long as all the saplings are the same type. (Mixing types can work, but the timing and space requirements get a bit messier.) You can add a torch in the middle to make the saplings able to grow at night and also ward off some mobs.