Old Tree Spirit

The Old Tree Spirit is a tree in the backyard of 742 Evergreen Terrace.

History
While in the treehouse, Lisa asked how she would get down. Bart then asked the tree to let them down. The tree did so, bending its trunk to lower the treehouse to nearly ground level, but then grumbled that the trees' life (specifically, their ability to move and talk) had been kept a secret for thousands of years until one fir tree let it slip.

Behind the Laughter
The Old Tree Spirit appears very similar to the s in The Lord of the Rings, in both voice and appearance.