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:
Diospyros rhombifolia, Diamond-leaf Persimmon
Edgeworthia chrysantha 'Snow Cream'
Illicium parviflorum 'Forest Green'
Illicium x 'Woodland Ruby'
Magnolia macrophylla var asheii