In Norse mythology, the tree that connects the Nine Realms is Yggdrasil. This immense ash tree acts as a cosmic axis, linking the different realms such as Asgard, Midgard, and Hel. Yggdrasil symbolizes the interconnectedness of all existence and serves as a bridge between the realms of gods, humans, and the dead. Its vitality represents the balance of life, encompassing themes of creation, destruction, and renewal.