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:
Cephalotaxus harringtonia 'Fastigiata'
Cephalotaxus harringtonia 'Fritz Huber'
Cryptomeria japonica 'Globosa Nana'
Epimedium pinnatum ssp. colchicum, Fairy Wings
Rohdea japonica, Japanese Sacred Lily
Viburnum plicatum 'Nanum'