(Hebrew עץ החיים) Although the Hebrew term is plural ("Tree of Lives") it is usually rendered singular.
"And out of the ground made the LORD God to grow every tree that is pleasant to the sight, and good for food; the tree of life [עץ החיים] also in the midst of the garden, and the tree of knowledge of good and evil." - Genesis 2:9
This tree represents the structure of the soul (microcosm) and of the universe (macrocosm).
"The Tree of Life is the spinal medulla. This Tree of Wisdom is also the ten Sephiroth, the twenty-two creative Major Arcana, letters, sounds and numbers, with which the Logos (God) created the Universe." - from Alcione, a lecture by Samael Aun Weor