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:
Leucothoe axillaris 'Dodd's Variegated'
Pieris japonica 'Temple Bells'
Poncirus trifoliata var. monstrosa
Primula vulgaris hybrid, Primrose
Viburnum plicatum 'Summer Snowflake'