The Tree of White Lilac Death was a necromantic construct, similar to a magical item or a ritual totem. It was constructed by Illiron.
The Tree of White Lilac Death served as a focus, able to gather charges from several deaths that happen at the same time and within a great distance from the tree.
Those death charges would appear as white lilac flowers, then made into Lilac Wine.
While the tree was destroyed by Liang, some bottles of Lilac Wine still exist.