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:
Viburnum plicatum 'Nanum'
Viburnum x burkwoodii 'Conoy'
Weigela florida 'Pink Poppet'
Weigela florida 'Rubidor', Pick-up ONLY