The Baron in the Trees by Italo Calvino (1977)

Can one live in trees whole his life? Meet Cosimo, the hero of this utopian story set in the 18th century, who one day decided to revolt against his family and traditions, and set to live in the trees. (Of course there were trees and forests spreading around at that time, as the book states) He rules his estate, meets Napoleon, corresponds with celebrities, and even has a love affair up in the sky. The book's ending is unusually fitting too. Delightful read for both adults and children.