That sounds like a disease whose name I forget. The first thing I would do is go back where I bought it and ask them. An ethical place would replace it if they sold you at diseased tree. However that might not be the problem. Unless they suggest otherwise, I would go ahead and cut off all the dead parts and dispose of them, either in the trash or burning if doing so is legal in your area.

It has been a dry spring here after a fairly harsh winter. If you have had the same, it could be too much stress on a transplanted tree. I am more of a dog expert than a tree expert. In almost all medical questions on dogs, I say take the dog to a vet. Somebody that knows trees and the conditions in your area might have a much better idea of the problem if they saw the tree.