Book had tree on front and Kingdom in title.

I am pretty sure the book has a tree on the front and it’s either blue or green. The title is “The ____ Kingdom,” I believe. It’s a fantasy book, because I remember there being magic. The plot was about a blind woman who’s city is under a giant tree. It may have been a series of books with unrelated characters. The book is at minimum, 9 years old. I have wanted to reread it for years but can remember enough, other than it was really great. Please help!