I got to thinking on the car ride home today(What a loser, right?) that the tree growth was a little...well just odd and make absolutely no sense. So I came up with sort of a timeline for tree growth.
To start,I believe the growth should be made much longer. This could be achieved by also adding half logs, or possibly even sticks. For example, I think the normal time it takes for a tree to grow FULLY in the space it's provided should just be changed. Perhaps one log with a stick(appears larger than it should) coming out of it. Or, have logs could be implemented as either large branches or trees growing at One and a half logs at a time(along with sticks and leaves)
Then,once the same period of time goes by, perhaps it now becomes two logs, a stick, and a block of leaves. This could be continued, and if untouched, the tree could grow to an incredible size. This would make it much easier for treehouses to be created, and could make for some great trees.
However, I believe all trees in the world that are generated should not grow as explained, only trees you plant.
Finally, I think bonemeal could now be changed as the growth is. The X number of bonemeal it takes to grow a tree in it's current condition now only makes it grow one level. This could be reduced, of course, as you can sometimes use an entire stack of bonemeal on just one tree.
I hope you strongly consider my ideas, and I hope some genius can find a better way to insert half logs. I am currently generating the idea in my head of a woodcutter. Fuel it by coal, like a furnace, and insert wood into in different forms to make different things, such as tables, half logs, steps, etc. If you think this is also a good idea, tell me and I'll make an entirely new thread using the best of my abilities