I think it's fair to say that when Richard Powers gets an idea, he runs with it. The Overstory is a novel about trees. Every other sentence mentions a tree. The main characters each have a signature tree. And most of them converge to protect trees. The structure of the book itself is designed to resemble a tree - each character has a backstory that is a root; the stories converge in the longest section - the trunk; the characters diverge again into the crown; and then in the smallest section they produce the seeds of a future world.
And my goodness the book is long and involved. Mo