The name of the Norse tree that connects the nine realms of existence is Yggdrasil. This immense tree is pivotal in Norse cosmology, representing the framework of the universe and the interconnectedness of all realms, including Asgard, Midgard, and others. Yggdrasil is often depicted as a giant ash tree, symbolizing life, growth, and the cycle of existence. Its roots and branches spread wide, embodying the complexities of fate and the relationship between gods and humans.