Here's a tree house. Built one block at a time, except for a couple of fill commands to change the logs to 6-sided and to place the structure_void and air blocks.
Tried to make it look like a natural tree that some built in and trims back branches for better views. I shaped the tree first and then built inside for a challenge. I like the outside, but the interior is kinda meh. Oh, and the guy that I imagine lives in this tree is also a fan of hiding treasure.
Here's a link to the structure download: