The Tree is an extremely large plant which has branches throughout the Basement, above ground, and within the Mansion's structure. Individual branches can be as large as ordinary trees. Such branches bear rounded crowns of foliage quite unlike the pine trees of the forest surrounding the mansion. The Tree provides breathable air, food, and even light to the basement. Light is supplied with the help of GBOLs.
When there is trouble underground, above-ground branches of the Tree can show symptoms. For instance, following the elevator fire and during the fighting in the basement, Amos described the Tree as "suckin.. blowin? kickin' up a fuss."
The Tree was created by Linus.