When I was building a tree stand I had 3 very tall white cedar trees to use. Since they were in a cluster of other trees they had grown quite close to each other and were thin for their height and tended to sway a lot in the wind.
I don't like putting single pivot bolts through trees, they work the hole bigger over time, moisture works it's way in, rot soon follows.
We've all noticed that when a fence wire is up against a tree the tree grows right over it. I though I might use this. I like the idea of using a log as the main beams, they last much longer than cut lumber in the elements.
I hoisted an 8" log up to the right spot, then wrapped a chain around the tree, out over and under the log, then back around the tree. I pulled the chain together and slipped a bolt through 2 links.
The links of the chain dig in to about 1/3rd of the circumference around the tree but they're large and smooth
enough that they don't cut in to the bark too much. It's been there for about 5 years and shows no signs of stressing the live tree.
In addition you're grabbing around the outside of the tree and the log, so you'll never have either one split from the stresses as you might when you bore a hole through the center. The chain is self tightening, just by the weight of the log and anything you put on it.
I'm hoping over the years the tree will grow right over the chain.
There a lot of peace of mind with this design. You never have to worry about inspecting the attachment points that hold
everything else up. Most of the log or tree would have to rot away before any kind of failure could occur, assuming your chain is of adequate size. You don't need that much chain either so go ahead and overkill on size if it makes you feel better.
This pic should make things clear(er).