A Treehouse Sukkah

In the case of one who establishes his sukka at the top of a tree or atop a camel, the sukka is fit, but one may not ascend and enter it on the first Festival day because the Sages prohibit climbing or using trees or animals on the Festival. If two of the walls of the sukka are in the tree and one is established on the ground by a person, or if two are established on the ground by a person and one is in the tree, the sukka is fit, but one may not ascend and enter it on the first Festival day because it is prohibited to use the tree. However, if three of the walls are established on the ground by a person and one is in the tree, then since it contains the minimum number of walls required, it is fit, and one may enter it on the first Festival day. The mishna summarizes that this is the principle: Any case where, were the tree removed, the sukka would be able to remain standing in and of itself, it is fit, and one may ascend and enter it on the Festival, since the tree is not its primary support.