It's not unheard of, that a unicorn may speak to a tree; unicorns love to live where the sun and moon dapple them through leaves, and unicorns do speak, though more often to each other, or themselves.
But the oak tree was not sure if it was meant to hear. The unicorn's eyes were full of leaves - the oak tree's own leaves, curled and cracked and bright with uselessness, ready for the wind to take - and she said, "Her hair was all of those colours, all at once."
Dull with approaching winter, too weary to rouse itself to reply, the oak let loose one leaf to fall on the unicorn, and both of them listened to the sound it made, scratching through her mane, and the sound she made, shivering beneath it (any sound a unicorn makes has somewhere deep below it a hint of bells).
Then the unicorn was gone.
The years ran rings around the oak tree's trunk, and the sun came through the oak tree's branches at a different angle, without passing through other trees first - but the unicorn, when she came again, was the same.
It was spring, then, and it seemed to surprise her. She reared up for her horn to touch one green leaf - and her touch was light, but sharp, like an insect's sting. "His eyes were exactly that colour," she said, "when he was smiling."
This time the oak tree held on to its leaf, but the unicorn didn't seem to mind.
The oak tree told the story to a family of squirrels, who told it to a crow, who told it to a rabbit - but that, in itself, is another story.
The third time the unicorn came, there was snow, smoothing out the snags of a tree that was lightning-blackened and stretched along the ground. Above the clearing that the oak tree's fall had made, a crescent moon shone, with a crooked smile that looked old and new, hopeful and sad.
She lingered a while in the clearing, between the old, dead tree and the young moon. If she said anything, then, the words have faded from the history books, or were never meant for anyone to hear.