Saw this on FB from the superb Texas Hill Country (great photography and more) and was reminded of one time on the Deschutes River when a friend pointed out a rattler in a tree near the water’s edge. I was oblivious that time, but some thirty years later I never fail to look upward too.
Bears and rattle snakes seem to like bird and squirrel feeders. Different food sources no doubt. So, some consider it more rare for a rattle snake to be in a tree, they (the various species) have a history of doing so.