Mix one part Jackass, one part John Muir, remove any sense of introspection, and run the self-preservation instinct through the wood chipper and you've got tree jumping. Let these young chap demonstrate:
So, to recap, here are the step-by-step directions for tree jumping. 1) Be a male in your teens or twenties; 2) Find tree of similar age and temperament a few feet from the top of a modest cliff; 3) stand at edge while friends goad you on off camera; 4) leap, grab on and try not to get jabbed in the kneecap; 5) stick the landing (no pun intended).
In fairness, these guys appear to be dedicated. They've got the nicks, scratches, and technique (grab with both hands, brace landing with feet to protect the manhood) to prove it. And it's kind of impressive--in a consequences-be-damned sort of way.