Yggdrasil has a rich history both in real-world Norse mythology and in the Marvel Cinematic Universe. In the real world, the tree is not only a prominent myth in one of the most well-known pantheons, but it is also a symbol of spirituality. Else known as the World's Tree, or the Tree of Life, it is known for connecting the cosmos together through time and space. Its existence in the MCU is first mentioned in Thor, and it was often hinted at throughout Phase 1 and in some instances in Phase 2. Taking into consideration the last episode of Loki season 2, Yggdrasil is being re-introduced in the MCU and its role has shifted from connecting the Nine Realms to connecting different timelines.
Source：https://www.cbr.com/mcu-yggdrasil-the-world-tree-explained/
