What is "treehouses"

Usage examples of "treehouses".

I thought that I remembered from the Cantos that the motile isles carried little except treehouses under their sail-trees.

They climbed the spiraling staircases of the big bamboo treehouses, and played hide and seek among the stacked rooms and the daughter shoots and the hanging bridges connecting them.

Just trees, treehouses and the occasional Elf looking down with interest at the procession.