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'
Buxus microphylla var japonica 'Borderline'
Buxus sempervirens 'Elegantissima'
Buxus sempervirens 'Unraveled'
Ilex aquifolia 'Night Glow'