I've added full directional control and the ability to specify something besides the joining distance for the vertical axis. I've also changed things so that the program doesn't use linestyle='steps' to make the branches, as a result you now have the ability to specify line styles for different branches in addition to color (useful if you're publishing in black & white).
If anyone has any suggestions for additional features they'd like to see, let me know and I'll see what I can do. If you'd like to write your own modifications, feel free to pass them along to me and I'll post an updated version that includes your modifications.
http://www.umit.maine.edu/~r.springuel/000CCFE8-80000018/
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R. Padraic Springuel
Teaching Assistant
Department of Physics and Astronomy
University of Maine
Bennett 309
Office Hours: Wednesday 2-3pm