What is the Tree of Life, first introduced in Gen 2:9, and why is there one? Is it symbolic?

It was the fruit of this tree that made Adam immortal when he was in the Garden; by being specifically cut off from the tree, he was made mortal. As Gen 3:22 has it, God evicted Adam “lest he put forth his hand, and take also of the tree of life, and eat, and live for ever”. The tree makes a reappearance in Revelation, which has the tree at the center of the New Jerusalem, “bearing twelve kinds of fruit…and the leaves of the tree were for the healing of the nations.” (Rev. 22:2) The tree will straddle a new river, like that of Eden. Evidently the symbolism is very rich: Jesus is called the “true vine” (John 15:1) and “the way, the truth, and the life” (John 14:6). Proverbs says that wisdom itself is metaphorically a tree of life (Prov. 3:18), as well as things that flow from wisdom, including desire fulfilled (Prov. 13:12), a healing tongue (Prov. 15:4), and the fruit of the righteous (Prov. 11:30). By placing this holy and life-sustaining tree in the Garden, God was specially blessing the innocent and sinless Adam; and it is only after being washed of their sins that man can again eat of this tree. Hence it seems to be a symbol for every sort of blessing one might have in a paradisiacal state in which one might dwell in God’s presence.