That's wild. I've never once seen this in the US.
Obviously there are people who just don't clean up after their dogs in the first place, but to clean it up and then hang the bagged crap on a tree? Haha.
It looks a lot nicer out there now and I gave the trees a little prune (I'm a qualified arborist) so people know this is a "tidy area" and so far no more turds in bags.
Each morning, I take a 5K walk around the neighborhood, and am constantly passing cast-off shitbags.
They are usually brightly-colored, and are easy to spot.
I remember, once, being at a stop light, on a fairly major road, where a guy was walking his dog, and just dropped the bag, right there. He did it kind of surreptitiously, but he still did it in front of everyone.
Probably was a fairly high-value person, too. It was a pretty tony neighborhood.