Definition of a Tree House Tree houses are not just for kids! Built high in the branches of a tree, a tree house is a typically wooden structure that utilizes the shapes of the trunk and the strongest boughs to create a horizontal space in a vertical world. They are accessed by ladders, occasionally linked by suspended bridges, and can even have running water and electricity. Cunning craftsmanship keeps these lofty rooms in their place and the rewards for the climb are peace and quiet, fresh canopy air, and spectacular views.