"Treehouse of Horror" is the third episode of The Simpsons second season, which aired on October 25, 1990. It was the first of a series of Halloween themed episodes, currently consisting of 18 episodes. The Simpsons Treehouse of Horror episodes are a yearly tradition. The Treehouse of Horror episodes generally do not obey the rest of the series' rules of realism, and are not treated as canon, although the first and third (and to a lesser extent, the second and fourth) are set-up in a fashion that they could be considered canon. In addition, since 1995, Bongo Comics has produced an annual comic book titled Bart Simpson's Treehouse of Horror.