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:
Acer saccharum 'Monumentale'
Aesculus flava, Yellow Buckeye
Aesculus pavia, Red Buckeye
Asimina triloba, Paw Paw
Chaenomeles x 'Bonita'
Fagus grandifolia, American Beech
Magnolia macrophylla var asheii
Magnolia x loebneri 'Donna'