The World Tree is a universal symbol of the different planes of existence. Common to many mythologies and religions is the concept of a World Tree whose roots reach down to the underworld and whose branches reach up to heaven.
The Norse have Yggdrasil, The Meso-Americans have the ceiba tree. Buddhist have the Bodhi tree, a tree under which Gautam Buddha meditated and gained enlightenment. Judeo-Christian beliefs begin in the Garden of Eden, and Eve’s incident with the Tree of the Knowledge of Good and Evil...etc.
The mythological symbol of the World Tree was a very strong one, and survived throughout the Slavic folklore for many centuries after Christianisation. Three levels of the universe were located on the tree.
"Yav" The world around us. Located at the middle of the World Tree the trunk. "Prav" Upper world the realm of heavenly deities and celestial bodies. "Nav" The underworld. Located in the roots of the World Tree. For Siberia the legends of the tree retained their importance for much longer time for it was tree that aspiring shamans climbed in order to gain their magical powers.