The Tree of Life was a part of mythology in many different Earth and Vulcan cultures. From the bottomless pit the roots of the tree of life would rise from Niflhel the underworld and its branches spread out through the heavens. Ancient Indian cultures called it Asvattha and the Scandinavians called it Yggdrasil. In the Vulcan culture it was called The Cosmic Tree and was known as the source of all plant life and eventually life on the planet.
On Stardate 8583.7 while exploring an unnamed planet, James T. Kirk, Spock and Doctor Leonard McCoy encountered the Tree of Life after they had completed a discussion on it. Kirk and Spock surmised that this planet was similar to the Amusement Park planet where thoughts became reality. When Spock was able to pull Kirk and McCoy out of their illusions, the tree disappeared. (TOS comic: "The Tree of Life, the Branches of Heaven")