Mankind and Yggdrasil
When the world was created, the first of humankind had to inhabit midgard. Odin, Vili and Vé carved the first of humankind from driftwood after they carefully placed him within the secure walls of what we call earth. The first man was called Ask and the first woman was called Embla. Ask meaning ash, Embla meaning elm both of which are names for trees. Not uncommon in Norse literature.
A gift from the gods
Ask and Embla had nothing but as said in Stanza 17 of the Poetic Edda they gained both Corporeal and Spiritual gifts. So Odin gave them breath and speech, Vili gave them consciousness and mobility and Vé gave them appearance and hearing. These 2 were to become the progenitors of all humanity within the walls of Midgard.
The world tree
The world tree, known as Yggdrasill, generally means ‘Odin’s Horse.’ This interpretation comes from the understanding of the word Drasill, which means horse and Ygg(r) which is another name for the Aesir Odin. Another understanding is the name of the tree itself, Yggdrasil, or Askr Yggdrasil meaning Ash (like Ask.) It would mean World Tree.
The world tree is mentioned multiple times in the Poetic Edda in the Völuspa, Hávámál and Grímnismál. In the Prose Edda, it is mentioned that three Roots span far and wide, one to Hel, one to Niflheim and one to Jotünheim. In the Middle is Midgard, where mankind lives.