Alright, history lesson. Jormungandr is NOT related to Yggdrasil at all. Jormungandr is a different name for the world serpent, the Midgards wyrm. You might know him by the name Ouroboros. The world serpent is one of Loki's three direct descendants, born between him and Angrboda. Tor, god of thunder, once tried to fish him out of the sea, though he was unsuccessful. The two are fated to fight during ragnarok.