The Tree of Life is an important symbol in nearly every culture. With its branches reaching into the sky, and roots deep in the earth, it dwells in three worlds- a link between heaven, the earth, and the underworld, uniting above and below. It is both a feminine symbol, bearing sustenance, and a masculine, visibly phallic symbol- another union.
In Jewish and Christian mythology, a tree sits at the center of both the Heavenly and Earthly Edens. The Norse cosmic World Ash, Ygdrassil, has its roots in the underworld while its branches support the abode of the Gods. The Egyptian’s Holy Sycamore stood on the threshold of life and death, connecting the worlds. To the Mayas, it is Yaxche, whose branches support the heavens.
The tree has other characteristics which lend easily to symbolism. Many trees take on the appearance of death in the winter- losing their leaves, only to sprout new growth with the return of spring. This aspect makes the tree a symbol of resurrection, and a stylized tree is the symbol of many resurrected Gods- Jesus, Attis, and Osirus all have crosses as their symbols. Most of these Gods are believed to have been crucified on trees, as well. The modern Christmas tree hearkens back to trees decorated to honor Attis, the crucified God of the Greeks.
A tree also bears seeds or fruits, which contain the essence of the tree, and this continuous regeneration is a potent symbol of immortality. It is the fruit of a tree that confers immortality in the Jewish creation story. In Taoist tradition, it is a divine peach that gives the gift of immortality. In ancient Persia, the fruit of the haoma bears this essence. The apples of Idun give the Norse gods their powers, much like the Gods of the Greek pantheon and their reliance on Ambrosia. This aspect of the tree as a giver of gifts and spiritual wisdom is also quite common.
It is while meditating under a Bodhi tree that Buddha received his enlightenment; the Norse God Odin received the gift of language while suspended upside down in the World Ash (an interesting parallel is the hanged man of the tarot). In Judeo-Christian mythology, the Tree of heaven sits at the center of creation, and is the source of the primordial rivers that water the earth-
The Tooba Tree of the Koran is a similar idea, from whose roots spring milk, honey, and wine.
This tree and its gifts of immortality are not easy to discover. It is historically difficult to find, and almost invariably guarded. The tree of Life in the Jewish bible is guarded by a Seraph (an angel in the form of a fiery serpent) bearing a flaming sword. To steal the apples of knowledge, the Greek hero Hercules had to slay a many-headed dragon Ladon. In Mayan legends, it is a serpent in the roots that must be contended with. Similarly, the Naga, or divine serpent guards the Hindu Tree. The Serpent Nidhog lives under Ygdrassil, and gnaws at the roots.
The tree as the abode of the Gods is another feature common to many mythologies; in some, the tree itself is a God. The ancient Sumerian God Dammuzi was personified as a tree, as is the Hindu Brahman. The Byzantine World tree represents the omnipotence of the Christian god.
Another form, the inverted Tree, represents spiritual growth, as well as the human nervous system. This tree, with its roots in heaven, and its branches growing downward, is most commonly found in Kabbalistic imagery.
A similar tree is mentioned in the Vedic Bhagavad Gita: “The banyan tree with its roots above, and its branches below, is imperishable.”
In Jewish Kabbalah, the inverted tree represents the nervous system as well- the ‘root’ in the cranial nerves, with the branches spreading throughout the body; it also represents the cosmic tree- rooted in heaven, the branches all of manifest creation.
Source : symboldictionary.net