Question
Is there a difference between trees and bushes? Is it a matter of height? I've seen bushes that could pass for small trees and large bushes that were shaped into trees. What's the rule?  

Answer
William,

It is realy in the eye of the beholder.

Bushes generally have foliage all the way to the ground while trees generally have a trunk.  Trees are generally larger than bushes.

Sometimes you might see a plant described as tree form.  This means a bush, probably a big bush, has had its lower foliage and branches removed to create a trunk.

Gary