The line between whether a plant is a "tree" or a "shrub" is sometimes very thin and quite blurry! We use the following criteria to decide which type applies to a certain plant:
Asimina triloba, Paw Paw
Chamaecyparis obtusa 'Well's Special'
Fagus grandifolia, American Beech
Magnolia figo 'Hagiwara Everblooming'
Magnolia macrophylla var asheii
Osmanthus fragrans 'Tea Olive'
Osmanthus heterophyllus 'Porcupine'