Building a treehouse is green, espcially, the one built by Ethan Schlussler.
He utilizes sheets of metal reclaimed from an old barn as roofing material and wood from the trees in the area it is built on. The treehouse is held in place by friction of five large cable clamps tightly encircled around the tree, so no nails, bolts or screws were knocked into the tree to secure it in place, 28 foot above the ground.
So, how does he gets up there? See for yourself.
That's a bicycle powered tree house elevator you are looking at!
He modified his mom's old bicycle with used parts and old scrap materials but to ensure that it works safely, new pulleys and cable were added.