A printed T-shirt from Charley's Greenhouses catalog for $20 sounds like a nice gift for someone who likes trees.
"Advice from a Tree"
Stand tall and proud.
Sink your teeth into the Earth.
Be content with your natural beauty.
Go out on a limb.
Drink plenty of water.
Remember your roots.
Enjoy the view.
Author: Ilan Shamir
P.S. I'd like to add one more line, another bit of free advice:
"Remember to feed and protect the birds."