There were two American Beech growing side by side in the forest 30 yards from our house that were grafted in such a way, via a single 3” diameter branch about 4’ off the ground. It is where I discovered chin-ups. It was awesome. I’d go down over the bank to this tree regularly, and go to failure as many times as I could. Inside narrow grip, inside wide, outside narrows, outside wide behind the necks, and side to sides. I was lucky to grow up in a home surrounded by hardwood forest, a creek, a river, and miles of open space.