The Tree isn't a mascot, but a band-member?...

There is no official mascot at Stanford. The "Tree," which is a member of the Band, is a representative of El Palo Alto, the Redwood tree is the logo of the city of Palo Alto. Since Stanford and Palo Alto are almost inextricably intertwined in interests and location, it is a natural outgrowth of this relationship. The tree still exists and stands by the railroad bridge beside San Francisquito Creek – it is the site where early explorers first camped when settling the area. In 1891, the student body actually voted for gold as the school’s official color, but another student assembly chose Cardinal as the school color. A few days after the vote, local sportswriters picked up the "Cardinal" theme after Stanford defeated Cal in the first Big Game(March 19, 1891). The headlines:, "Cardinal Triumphs O’er Blue and Gold." Cardinal was the school color until the 1940’s, when rules committees and conferences started regulating jersey colors for home and visiting football teams and added white.

http://www.gostanford.com/school-bio/stan-nickname-mascot.html