What does a tree of life symbolize?

In very basic terms, which are all I can provide, the cabbalistic tree of life is a very rough and basic map of the universe. There are many known uses of the tree, one of which is as a meditation tool. Each of the ten branches are symbolic of ten basic principles of the universe. These Sephiroth were originally named after principles of the Godhead; Beauty; Wisdom; Compassion; etc. Through following the pathways between the principles (psychically), the aspirant to enlightenment goes deeper and deeper into the psyche, uncovering , or discovering rather, facets of the true self that lies dormant beneath his/her everyday facade. Please forgive this bare bones summary, what it lacks in detail is more than made up for with its' brevity. For further info check your local bookstore. There are literally hundreds of books out on this subject.