Yggdrasil

The world ash, "The best of trees", wet with white water and green by Urth's well, with three roots over Hel, the frost-giants and mankind; the gods ride to it daily to give judgment; a squirrel, four harts, an eagle and the dragon Nithhogg live on and under it; it shakes when Ragnarok comes. Odin's "windy tree" of the Hovamol is generally taken to be it.