This sort of looks are normally due to root-problems. Over fertilizing, drying out, overwatering etcetc. Dificult to judge which.
Taking it out of the current container, and placing in a larger pot, without messing with the roots, often helps a lot in solving the problems. I personally think this tree is too far gone to rescue unless you know really well what you are doing.
Main thing: Do not handle more than needed. Do not fertilize untill you are certain it has recovered.