This is one of the best tree houses I've ever seen. Kudos for a job well done!
"To get the most support with the least likelihood of hurting the tree, you want to use fewer, bigger bolts (rather than a lot of smaller screws or nails). These are 1.25” diameter, 15” long galvanized lag bolts, 4 of which will bear the entire weight of the treehouse. In my case that total was roughly 1,000 pounds, a tiny fraction of what these bolts will hold. This is the general idea when putting kids at height: overbuild for safety."
"The treehouse platform frame is a basic deck construction, but done with 2x6s to save weight — and 12” on-center to maintain strength. I framed in a trap door opening, and built using joist hangers and nails. I used a $49 cordless palm nailer, because I’m bad enough with a hammer on the ground, much less swinging it at odd angles 30 feet in the air. I’ll never go back to a hammer now if I can use the palm nailer, BTW."