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:
Abelia chinensis 'Compact'
Aesculus flava, Yellow Buckeye
Aesculus pavia, Red Buckeye
Edgeworthia chrysantha 'Snow Cream'
Philadelphus lewisii 'Fallbrook'