I guess I really like tree houses because
here is a link to a cheesy website with a cheesy mission statement offering (for a price) a stay in a tree sphere. Below are some photos of the spheres.
below is a more spacious Vietnamese tree house. More information about that can be found
here.
Finally,
Here is a portfolio of O2 Treehouse. Some interesting ones can be found there, but I've uploaded my favorites below: