Tree Girl by T. A. Barron

But mostly he just plays in the branches. He hangs in them, swings in them, and swats them—until the branches swat back.
    And sometimes, that bear is joined by another—a brown bear who romps through the forest with her friend. Who races through the sunlit groves, always ready to wrestle. And who loves nothing more than to climb a tree.
    Whenever breezes sweep across the ridge, the two willows weave and sway as one. Their leafy boughs, falling like tresses by their sides, move in a dreamlike dance. And while the willow trees dance, they make a song all soft and slow and whispery.
    A song that blows like the wind, and beats like a heart.