The Overstory by Richard Powers won the Pulitzer Prize and is a novel about trees, which is true but incomplete. It's also a novel about activism and how people come to care about things that operate on timescales they can't perceive. The trees in the novel live for centuries. The humans live for decades. The gap between those timescales is the subject.

Powers structures the novel as nested stories — individual character histories that converge on a common crisis — and the structure is itself an argument about roots and branches. Each human storyline is a root of the larger narrative. The metaphor is heavy but it earns its heaviness because the novel has done enough character work for you to feel the weight.

What I remember most is a scene involving a chestnut tree that has survived the blight that killed all the American chestnuts, and the family that has photographed it across four generations. It is a long sentence and it is the best single passage in the novel.