Just as a PSA for everyone who is also encountering glitches with this tomb: just as this video shows, make sure to completely avoid burning the tree at the very center of the plane. Doing so causes the glitch that restores the remaining tree's collision thus not allowing you to pass through the back piece of the plane and reach the treasure. As far as I am aware, this glitch only affects the Steam version of Tomb Raider 2013. Normally you are supposed to burn everything burnable, but not here.