One of the key factors that distinguishes bushes from trees is the height of the main stem. In general, bushes have main stems that are less than 10 feet tall, while trees have main stems that are taller than 10 feet. However, there are some exceptions to this rule, such as the dwarf Alberta spruce, which is a tree that typically grows to a height of only 4 to 6 feet.
Another factor that distinguishes bushes from trees is the shape of the canopy. Bushes typically have a rounded or spreading canopy, while trees have a more upright or conical canopy. However, there are also some exceptions to this rule, such as the weeping willow, which is a tree that has a drooping or spreading canopy.
Ultimately, the distinction between a bush and a small tree is not always clear-cut. There are many plants that fall somewhere in between these two categories, and it can be difficult to say definitively whether they are bushes or small trees. However, by considering factors such as the height of the main stem and the shape of the canopy, we can generally make a determination.