The tree in this picture is gigantic like it's bigger than any dragons seen before (so don't be greedy and try to be bigger than a tree). Now this tree not only part of the dragon next but it's last part of Gaia. Since during the fight between Gaia and her brother (after the death of Ciri) Gaia use a forbidden spell to seal away her brother. Her body and soul become the tree itself as her brother is locked away somewhere in there. It is unclear that Gaia is alive or hot but regardless of that it serves as a protection for the dragons and a symbol of hope. So in other world meet with each other and have fun.