I've been recording a 100 Day Tutorial with benchmarks or milestones; because minecraft can get monotonous and/or directionless. Its after playing minecraft with my 8 year old son and he kept on creating new worlds rather than developing an existing one. I think he likes the initial challenge of the start up; but he lacks the patience of mining for diamonds...
Anyway the 100 day tutorial is based on 100 minecraft days ~ 25 hours of play. It goes into:
a) setting up house (on an island);
creating crops (wheat);
c) creating a shaft mine (to the bottom);
d) creating a farm (cows and chickens);
e) mining for iron; exploring dungeons/caves;
f) being an explorer bring samples of your world back to your farm (and planting these items if possible);
g) preparing for the nether;
h) making traps and redstone devices;
i) mining for diamonds; excavating around lava pits.
(up to day 55 out of 100).
Anyways back from the segwey - two important discoveries about trees.
1. They can grow inside a cave; as long as there is heaps of light (from jack-o-lanterns) and space for the leaves; adjacent to a water block; sapling planted on dirt.
2. Trees can grow in the nether :-O. You need to clear out any nearby fires; plant the sapling on a dirt block.