Well the base supports, floor joists and floor have been installed. The entire structure sits 10 feet off of the ground.
All the corners were braced with a section of 4" x 4" post. There are 3/4" carriage bolts with split washer, washer and nut on each. there are two bolts per side. Where the supports contacted the tree, 3/4" x 6" lag screws were used. I tried to put at least two in everywhere that contacted the tree to alleviate any cantalever.
We have had several bad wind storm and nothing moved. Lots of creaks and moans from the tree/supports, but no damage.
Once the entire base support system was installed, I began spacing out the floor joists using standard joist hangers rated for treated lumber. The base support systems is mainly constructed with 2" x 6" boards, but there are two 2" x 12" supports next to the tree. All of the floor joists were treated 2" x 6" lumber. Rated 10d nails were used to attach the joist hangers and the joists. Oh, and I did add some 2" x 6" diagonal supports to the 4" x 4" posts. It was impossible to bury the posts due to the amount of roots around the tree, but the posts are set on concrete pads to disperse some of the weight.
Once all of the floor joists were in place, 3/4" plywood decking was used for the floor base. This will be covered at a later time with something a little more decrative and functional.
Of course my girls had to try out the floor with me!