The Tree of Life is a location that is home to Rani, Kion, the Night Pride, and many rare animals. It is the true home and origin of the Roar of the Elders. In Season 3 of The Lion Guard, along with Makini travel there to heal Kion and Ono's wounds.
The Tree of Life is a safe-haven where animals from everywhere come to heal or if they are of an endangered species. Rafiki told the Lion Guard about it near the end of Battle for the Pride Lands. They hope to receive help for problems for which they can't find any solutions elsewhere. The Tree of Life has all kinds of animal habitats.
The Tree of Life appears to have mystical powers, as Queen Janna channeled its energy to help heal Ono's eyes to restore his vision. Though this power appears to have limits, as Janna could not restore Ono's vision to be as keen as it used to be.