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:
Abies firma, Japanese Fir
Abies pinsapo 'Aurea', Golden Spanish Fir
Abies pinsapo 'Glauca', Blue Spanish Fir
Aesculus flava, Yellow Buckeye
Aesculus pavia, Red Buckeye
Aesculus x splendens
Asimina triloba, Paw Paw
Cedrus deodara 'Eisregen', Hardy Deodar Cedar
Chamaecyparis lawsoniana 'Wissel's Saguaro'
Chionanthus retusus 'Tokyo Tower'