source article: http://www.byzant.com/Mystical/Symbols/OtzChiim.aspx
Otz Chiim, the Tree of Life, is the symbol at the heart of the Kabbalah. It encapsulates creation, existence and the return to the Divine (or the path to enlightenment). The Tree is built from thirty-two "paths" comprised of ten sefirot and the twenty-two paths through which they interrelate. The twenty-two paths correspond to the letters of the Hebrew alphabet, and in the Western Kabbalah they are normally drawn as shown in our discussion of the Tree of Life. In Judaic Kabbalah, the paths usually differ slightly, being placed as shown in the Tree above. In this Tree, there are no direct paths between Malkuth and Hod or Netsach; instead there are paths between Binah and Chesedand Chokmah and Geburah, mirroring more closely the "lightning flash of creation" in which the sefirot are emanated sequentially, each from its predecessor.