Peter "Tesladownunder" Terren first experimented with the idea of making a Christmas tree out of a Tesla coil and some fancy photography back in 2007. He decided to go bigger and more colorful this year, and the results are pretty impressive.
From Mr. Tesladownunder:
This year I did another Xmas tree based on the success of the one I did in 2007. I made it bigger (9m = 30 ft) and more spectacular by using a different technique. It still uses a long exposure and a rotating colored filter but the tree shape is outlined by sparks from a rotating rod on top of the Tesla coil. This gives the "Eye of Sauron" effect. Imagine then if that rotating rod is able to be raised from horizontal to vertical while still rotating.
See how the 2009 Tesla coil Christmas tree came to be in the gallery below, and check out his website for a detailed account of how he did it.