shade tree that won't drip sap
I am looking for a tree to plant in the front(North side of my house), that will not dip sap on my cars. I currently have an alder that makes a mess. I don't mind leaves, it's the sap and pollen that I would like to avoid. Size is not a problem. The area, 70' X 30' is a natural garden with a crushed gravel drive. It is a shady location with a large fern garden. I do like the look of Himalayan birch, however, not sure if it's messy? Stewartia is always beautiful.
Any suggestions would be gratefully appreciated.