Have you ever seen the TV show, "Treehouse Masters"? This contractor custom builds amazing treehouses for clients all over the US. These often are party pads with plumbing, kitchens, etc. Some of these are in rural locations, but many of these structures are in cities.
NEVER does the show ever refer to a building inspector. I'm waiting for the city inspectors to show up and declare the structures illegal and force the owners to tear them down. There are substantial investments in these dwellings.
As much as I'd like a treehouse, I'd never build one on my property. Every spring in Wisconsin, I lose 2, or 3, trees to the weather. Often there is no warning. My house is 50+ years old, and I've noticed that that is when the trees start falling, although I have neighbors who have lost trees at a younger age. My friend lived in a house in the woods that is 80+ years old. She even lost oaks annually. Provided an endless supply of firewood.
The red oaks on my land seem to fall a lot. They don’t seem to have much of a tap root.
The show is on one of the liberal channels, IIRC, and they'd never show that kind of government intrusion. I'm sure it happens behind the scenes. I think this is on Animal Planet, one of the worst PC offenders.