Q.Apple tree , one half dying
Two major branches on one side appear dead, with no blossoms at all. Other branches are showing lots of blossoms.

Certified GKH Gardening Expert
There are several diseases that can cause branches to die on apple trees. One of the most serious is fire blight, which you can learn about in this article:
http://ipm.ucanr.edu/PMG/PESTNOTES/pn7414.html
Black rot limb canker and collar rot are other possible causes. See the following articles for more information:
https://www.gardeningknowhow.com/edible/fruits/apples/apple-tree-diseases.htm
https://www.rhs.org.uk/advice/profile?PID=769#section-3
You may want to contact our local extension office for help figuring out what is wrong with your tree and whether it can be treated.