Additional photo

One more photo

Bit hard to work out from the photos what exactly is happening. The best I can make of it is that some species of wood boring grub is in the tree. Could be wasp or beetle larvae. I don't know which ones you might have there but probably best you check with your local agricultural department. Termite damage can also look like that but do you have termites there? If it were here I'd say Mastotermes darwiniensis, but not in Singapore.

if it's a boring insect, cut off all affected branches below the damaged part. Bag and take to the dump, don't put in compost or green waste, that will just spread the bugs.