Money tree rot is caused by a fungal disease called root rot. In a tree, root rot usually starts as a small area of yellowing and wilting around the trunk and lower branches.
Once a money tree gets money tree rot, it becomes hard to tell whether or not it will die. Money tree rot is often fatal to the tree and usually kills the entire tree.
The easiest way to diagnose money tree rot is simply to look for the telltale signs: yellowing leaves and trunk, discoloration, etc. But there are other, more subtle signs of trouble too, such as wilted foliage and dry branches.