The size which is known as the mature size of the tree is the only difference between a crepe myrtle bush and tree.
Other than the mature size of the crepe myrtle bush and the crepe myrtle tree is the size it grows too when it matures.
A crepe myrtle bush and a crepe myrtle tree are the same thing but the crepe myrtle tree grows larger than the bush does.
The wood is basically the same thing for the crepe myrtle bush and the crepe myrtle tree.
Crepe Myrtle Trees are commonly used to make wood crafts such as wood canes.
My Grandpa made himself a Crepe Myrtle wood cane and they do make good walking canes.