I have a small tree which I've identified as a Malabar chestnut through google images. It is about twelve years old, a plant I rescued when my work office closed about two years ago. I've changed the soil when I brought it home and it has been doing well in my humid Brooklyn apartment. It gets indirect sunlight. Very recently, one of the branches has started to die off. All of the leaves have wilted and the wood part feels slightly softer than the other two. I water once a week. Is there anything I can do to rescue this part of the tree? Any further help of care would be appreciated.