Here’s a another interesting treehouse, one that hugs a tree! This was found via http://www.treehugger.com/files/2010/01/flatpack-treehouse-is-dutch-treat.php. Here’s a brief blurb:
What I really love is the simplicity, the way it fastens together with the ratchet straps; just crank them tight and they hold the thing together and onto the tree. The dutch bracket on the front is the only thing that doesn’t fit this pattern, but of course they had to have it.