Excellent stuff is always coming from mr Grant Skinner. He is one of the best Flash developers out there, always pushing limits and handing out something interesting.
Branching tree experiment is kind of experiment that many people tries to do perfectly, trying out to push the limits to the realistical looks. Grant Skinner did it amazingly and expectedly great. Check out his Elm Tree Branching Experiment
There you can find links to his previous experiments in branching, circular and previous tree branching in as2, check them out too.
Respect for gskinner!