Yggdrasil - The World Tree
The great ash tree Yggdrasil connects all nine worlds and stands at the center of existence.
Yggdrasil, the World Tree, is the axis of the cosmos. Its roots reach into three wells, its branches hold the nine worlds. Eagles nest in its crown, a serpent gnaws its roots, and squirrels carry messages between them. All existence depends on Yggdrasil's health.
I know an ash, Yggdrasil by name, a tall tree wet with white water; thence come the dews that fall in the dales.
Yggdrasil represents the interconnected nature of all existence.
Poetic Edda