I have seen a number of wrap around benches over the years, but I haven’t come across a plan before. I must admit that I wasn’t exactly out there looking. It seems more like a 1970’s deck item, but it is a still a fantastic use of space in a back yard.
This free wrap around plan is from This old house. The plan is well laid out with many photos and an exploded drawing. Your plan might vary a bit based on the size of your tree, but the plan should help you to address any math that is required.
Good luck with your own wrap around tree bench.