The World Tree is was an early, non-literal model of the universe among many cultures. It stretched from below the ground, and held up the sky, with our surface world in between – in middle earth.
The World Tree is a symbol for the interconnectedness of all things. Though roots may never see the light of the sun, they are nonetheless fed by leaves at the top of the canopy. The leaves, in turn, quickly wilt without the support of the roots below.
For the Norse, the World Tree was known as Yggdrasil, a gigantic ash tree upon which Odin was crucified so that he could gain deeper wisdom. Odin also sacrificed one of his eyes to a dwarf-dragon Mimir (memory), living among the tree’s roots. In Hinduism, the Asvattha, a kind of fig is an aspect of Brahman, the fundamental cosmic identity that underlies all things. The Buddha was said to sit under such a tree in order to attain enlightenment.
Other cultures identify trees as the source of humanity. Algonquian Native American groups and Persians alike told stories of the first humans being carved from trees.
In our own times, the cultural movement of environmentalism has also adopted the World Tree as one of its symbols. The World Tree tshirt you see here is printed on organic cotton, and made here in the United States, following that theme.