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:
Buxus microphylla var japonica 'Borderline'
Cephalotaxus harringtonia 'Gold Rush'
Magnolia x loebneri 'Donna'
Smilax biflora var biflora