Ilyanoryth

The tree was absolutely beautiful. Tall and stout, covered in smooth golden brown bark, the branches stretched upwards into a wonderfully round shape, like a rising sun. The leaves gradiated from red to yellow, bottom to top. It was both the most real and most unreal tree that Emma had ever seen. She couldn’t even tell what kind of tree it was.

The Ilyanoryth is insanely important when it comes to the magic of Midnight Town, and especially when it comes to the fae. As its caretakers, they both receive greater benefits from its magic and worse consequences if something happens to it.
It's an entirely unique tree. While there are other such guardian trees, the Ilyanoryth is the only specific one of its kind, and would be genetically distinct from others, were a human scientist to get their hands on some DNA from two such guardian trees. Its current guardian is Jennifer Lemagre, which is partially why her parents ended up on The Council.
When it blooms, it becomes a source of some unique energies, which also makes it something of a target from outside forces. Its life cycle is not easily tracked by anyone not intimately connected to it, which provides some protection.
The foundation of the tree is carved with arcane symbols to further tie its guardian to it. This allows the guardian to draw on its power, but also allows the guardian some degree of control over where the tree is.