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:
Ginkgo biloba ‘Chase Manhattan’
Ilex aquifolia 'Night Glow'
Ilex crenata 'Piccolo', Dwarf Japanese Holly
Illicium parviflorum 'Florida Sunshine'
Mahonia eurybracteata 'Narihira'
Picea orientalis 'Skylands'