From Youtube:

"n 1974, fresh out of the army, Michael Garnier went to rural Oregon to try to make a living off the woods. He tried making furniture, fences, pole barns and selling organic, psychadelic picture propellers (to see Fantasy Flakes), but finally it was a treehouse that got him all the attention.

Modeled after the treehouse he had once built for his kids, his first treehouse B&B was completed in 1990. Today he has 9 treehouses for rent, 20 staircases, 5 or 6 bridges, several platforms and zip lines for rapid descent and at least one fireman's pole. Some of his treehouses even have toilets, running water and showers, though he warns guests to "stand when they flush".

Over the years, Garnier has become legend in his industry and helped invent a better way to build a treehouse. Instead of bolting wood to wood (i.e. beams to the tree), Garnier and his colleagues at the World Treehouse Conference (an event he used to host) developed a way to attach steel bolts and cuffs to the tree.

Dubbed the Garnier Limb (or G.L.), this open source design can support 8,000 pounds. Garnier sells GLs of all different types as well as plans to build your own treehouse. His DIY treehouses are for 12 foot trees ($150) and he sells about 30 or 40 plans per year."