Greening Milwaukee is a non-profit organization dedicated to, well, doing just that! Making Milwaukee greener by showing people how easy it is to plant trees and how planting trees can have many positive effects- both on people and the environment. And they'll be happy to give you a tree - for free!
Arbor Day Foundation is a non-profit conservation and education organization with a million members, donors and partners worldwide. They offer affordable trees and seedlings as well as planting and care guides and free landscape guides.