Or maybe something more like this?
http://www.inhabitat.com/2006/08/31/4treehouse-by-lukasz-kos/#more-1079
I like the idea of having it above the ground, maybe suspended. Also a bunch of other cool ideas here:
http://www.inhabitat.com/category/treehouses/

In reply to this comment by Peroxide:
I dream of building my own tree based house, sort of like this one, but perhaps with a center beam that is a living tree, ( i know, i know, the roots would need water...)

http://www.simondale.net/house/

Everything makes perfect sense, except for the building codes that prevent anyone from making their own house.