Pull back the high spot of soil around the base of the tree. Remove about two or three inches of soil to allow the roots to get oxygen deeper. Cut the water and don't put any on it until the top 5 inches of soil is dry. I think you can still save it if you allow the roots drying time. Loosen the soil all the way to the grass edge and keep it loose after every rain. Here is a photo of a healthy root flair, and what you want, can you see the difference?