Yesterday, I spent about an hour working on this mod. I got it so that the growth blocks will grow new trees with growth blocks on top. Unfortunately, they wouldn’t grow continuously, due to a bug that I know exactly how to fix, but didn’t have the time yesterday.
I just started this mod today, although I spent a few hours yesterday learning how to use minecraft forge. Currently the mod adds one block, exactly identical to leaves. Eventually, the block will provide the basis for this mod, as it will be what generates new tree branches. Here is the link to the suggestion that this mod is based on: http://www.minecraftforum.net/topic/47316-tall-trees-short-trees-and-a-way-to-make-them/