We had a tree house when I lived in New York about 40 miles south of Buffalo, it was only up about 6 feet, where there was a large fork in a large tree, fully enclosed, 'no goils allowed'
, all that stuff, but, that winter a blizzard split that tree at the fork, bring both halves of the tree down and the tree house with it.
That next summer we dug an underground clubhouse down into a large mound across the street, the mound had been there as long as we could remember ('we' were not that old, though), and after using it for awhile, our parents discovered what we had been doing and forbade us from going down in there because it might cave in on us. (Of course, though, when you forbid a kid to do something ... ). Later that summer, during the heavy rains ... yep, it collapsed in on itself. That mound had been there a long time - with support in its center, but it did not last the summer after its center had been dug out.
Tree houses, caves, you name it, we did it, and we survived to tell about it.