Angel, what part of the world are you in? I ask because Magnolia champaca is a beautiful tropical to semi-tropical tree. If you don't live where M. champaca are naturally grow and you had the tree outdoors, it's possible the winter was colder than usual in your area and the tree was killed.
Please provide more info to your location (be specific - don't name the state or country only), how old and how tall your tree is, and whether it's planted in the ground or in a large container.
In the meantime, you can check whether your tree is alive or not by cutting off one of the thinner side branches. Look at the wood. Is the inner growth and bark dry and brown or is it green and flexible? If it's dry and brown, check some other thin branches to see if you can find live wood. Just because the roots aren't black and decayed looking doesn't mean the tree is still alive. Woody matter like tree roots take many years to decay and appear fine for a long time.