Since I built the Tree House some years ago, it has remained relatively stable. I did adjust the height of one support by about an inch a year or so ago just to make the house level again. I think that one of the branches upon which the Tree House rests has actually lowered by an inch or so. That was a relatively minor adjustment that was accomplished with a jack and a shim under the support pole.
Now, this last winter we had some pretty severe storms out here and I believe we had one storm where the winds were up to about 82 MPH. That's Level I hurricane winds. Consequently, the cable that I had strung from the large Pine tree to the Tree House, which is suspended from the Oak tree, was pulled out of its mooring in the Pine tree. This resulted in a minor amount of sway in the Tree House. I had put in that cable to eliminate the sway. It wasn't too bad without it. It was more like being on a boat and pitching and yawing in the swell.
Anyway, I went out to the hardware store and got a much larger anchor for the Pine tree. Originally I had installed an eyebolt. The problem with an eyebolt is that at the base of the eye portion, there is a seam, and, as it so happened with that much force on it, the eye opened and the cable was released. I replaced the eyebolt with a larger bolt with a metal tab with two holes in it. One hole is what I put the new bolt into, and the other hole is where I passed the cable through. It took a few hours to get it reinstalled. The biggest problem was getting the 10" bolt into the tree. I drilled a tap hole. I didn't want to make the tap hole too large, and when I went to screw in the bolt, the force needed to screw it all the way in was tremendous. I had to get out a very large and special-purpose drill to make it go in all the way (30 feet in the air on a ladder).
Since I have installed the new bolt, there has been no noticeable sway in the Tree House.
Job done.