At this point the OP has to find a tree and check the local requirements to have a CO (Certificate of Occupancy) issued or equivalent if required. If not required I doubt an insurance company would provide a homeowners policy for a treehouse, though perhaps other kinds of coverage, but probably at a high price. The difference between a treehouse and a pit full of boards with nails sticking out means nothing to an insurance company without some 3rd party attesting to it’s safe use as a residence.
The OP’s examples are not actual tree houses, they’re just houses on stilts. The foundation could be poured concrete with wood and steel above, or they could be treated wood piles. The photos try not to show that too much, but one of the homes is on a steel frame. There’s nothing particularly novel about that. Coastal homes in hurricane country or homes on hillsides are built like this all the time. These even look conventionally framed, just with wood plank interior walls and faux log exteriors with typical roofs and windows. They may have an increased fire risk in fire-prone areas, but they also have a reduced flood risk. Thermal performance won’t be quite as good a a conventional home because they’re above ground, but insurers don’t really care about that.