The Tree of Life was planted by Satyr from a seed he brought through from beyond the Gates.
The Tree extends throughout almost the entirety of the Dreaming, except Arcadia. Few realms do not contain a root or branch or leaf of this greatest of all trees. A part of one branch extended even into Ironfell; when that place split off entirely from the Dreaming and became the mortal world, the branch remained, though it was petrified.
The tree moves (except in Ironfell, and its movement creates the wind that blows the souls of dead fae through the Dreaming for the Sluagh to find.