The ‘World tree’ is inspired by the Norse legend of Yggdrasil. In Norse mythology Yggdrasil is an immense tree that is central in Norse cosmology, in connection with which the nine worlds exist. Yggdrasil
is attested in the ‘Poetic’ and the ‘Prose’,  compiled by Edda, in the 13th century from earlier traditional sources.
In both sources Yggdrasil is an immense ash tree that is central and considered very holy. The gods go to Yggdrasil daily to assemble. The branches of Yggdrasil extend far into
the heavens, and the roots extend far into other locations; Creatures living within Yggdrasil, including the wyrm (dragon), the eagle and the stags.