So, this sad tree has a lot of meaning to it once you play the game.
The general idea of the game is that masks have the embodiment of a soul, and when a person dies, their mask has the ability to give you a new ability.
For example, Darmani (Goron Hero) dies and you then receive his mask to change into him, the same with the Zora. What this means is that that tree a Deku Scrub that was killed to turn me into a Deku.
More on that later, but it gets sadder and sadder. The plots so good.