Crab Apple tree not growing

Hi, I have a crab apple tree which is about 4 years old. The first two years, it grew fine. Then last year, leaves/apples/flowers only grew on some branches. Others had nothing. This year not one thing as grown. I don't even see any buds. Any idea what may be happening? Most branches look dry and dead. Thank you kindly.

 

Apparently started to die last year and this year the process has been completed or nearly so.