For my Masters degree I used a canopy crane to study sugar maple canopies in Haliburton, Ontario, so it goes without saying that I am fond of trees.
Check out the beautiful tree house cafe designed by Pacific Environments Architects.
You should really take the time to peruse these amazing drawings and conceptual sketches!
Here is another beautiful example, albeit minus the engineered beams.
More details and photos from weburbanist.com
Also interesting is a modern example from Baumraum tree houses (tree room in Deutsch).
Have a good weekend, and get outside if you can!