I really enjoyed this video of a guy who has created a series of tree houses in Oregon. A lot of the video is about the houses themselves, which is very neat, but I especially liked when he discussed the different mounts he invented to keep them in the trees.
He shows off several of the mounts and attachment points towards the end, and how they move with the tree – when the trees start swaying in the wind, you have to have a mount which allows some freedom of movement. This is especially true when you’re talking about a bridge between two trees which has to account for movement of both trees.
He even uses the phrase “open source” in there, about how he worked with another engineer to design these mounts, and you can presumably use the same designs.
(One of the tree houses he shows off has what appears to be a full-size, standard toilet. I’m dying to know how that works.)