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:
Cornus sericea 'Neil Z'
Fagus grandifolia, American Beech
Picea glauca 'Gold Tip'
Salix purpurea 'Pendula'
Syringa chinensis 'Tiny Dancer'
Syringa x "Red Pixie'