A late addition to this topic, but then I did only find the website a few days back!
I used to study martial arts and we did indeed practice falling out of trees (actually, we were practising running up trees, but obviously learning how to cope if it goes wrong comes first!).
Running up a tree is easy; I'm sure many of your have tried running up walls or trees in your youth. Basically, you run at the tree at a moderate pace, and once you get to the _base_, you run up the tree. You need to keep your body close to the vertical and just keep pumping with your feet. Anyway, you'll either get to the first branch and manage to hang on, or you won't. Assuming the latter happens, when you fall you will be facing the tree. You need to angle your body by pulling one foot backward (think snowboard / skateboard if you're not sure which one). Ideally, when you hit the ground, you should have your feet shoulder-width apart and at an angle of around 45° to the trunk, and your legs slightly bent. As you hit the ground, you need to absorb some of the shock by flexing your legs and carry your momentum into a roll over your rear shoulder. Ideally, you should be fully familiar in the various types of rolls by repeated practice on the ground before you even think of doing it from a height.
Of course, the advantage you have when performing this type of exercise is that you are ready for a fall. If you suddenly find yourself plummeting from a height with no warning, I'm not convinced that you'll have a great deal of say in how you hit the ground. However, repeated practice, until the art of rolling from a fall becomes an automatic response, can only increase your chances of minimising injury.
It goes without saying that if you decide to try practising falling from trees and end up doing yourself a nasty, you'll only have yourself to blame
