Amirdrassil (meaning Crown of Harmony in Darnassian) is a World Tree currently growing within the Emerald Dream. It is meant to become the night elves' new home on the Dragon Isles.
When Elune (through Tyrande Whisperwind) and the Winter Queen communed in Ardenweald, they created The Sisters' Tear, an artifact meant to serve as a "vessel of renewal". The souls of the night elves who died during the Burning of Teldrassil and who were rescued from the Maw chose to become part of "a new beginning for their people" and entered the vessel, forming a new "seed", touched by both the Dream and Ardenweald and embodying the cycle of Death and Life. After the rediscovery of the Dragon Isles, Tyrande brought the seed to Merithra, who took her through the Ancient Bough so that she could plant it within the Emerald Dream for safety.Guarded by the green dragonflight and the defenders of the Dream, it peacefully grew into a giant World Tree.
When the time neared for the tree to leave the cradle of the Emerald Dream and manifest into the physical world, the Primalists set their eyes on it. Ice Primalist forces led by Rymek infiltrated the Emerald Dream and attempted to locate the nascent tree but were defeated by Ysera, who had returned from the Shadowlands to defend the Dream. After the defeat of the infinite dragonflight, Nozdormu saw a vision of burning embers and Fyrakk attacking Amirdrassil. Alexstrasza sent a warning to Merithra to prepare the green dragonflight's defense in order to protect the growing World Tree.
Thanks to their new allies, the Druids of the Flame, Fyrakk and his forces finally made their way into the Emerald Dream. But rather than destroy or burn it, Fyrakk set out to imbue the tree with "the living flame", spreading it across all of Azeroth and remaking the world in eternal fire.