What is happening to my Citrus Tree?

Dear Members,
My 7 year old citrus tree suddenly started shedding leaves, green branches started dying back, all flowers also withered away, fruits that remained also dropped. The tree is planted in area with full sunlight outdoor.

This started 2-3 months back when just few branches were dying back, which I removed from the tree, now the condition is getting worse.

I am unable to spot the issue (some pest or root fungus). I have sprayed Malathion diluted water mix spray on its leaves/branches and even put malathion in roots after digging. But it didn’t seem to help.

The issue seem to have affected other plants in my garden too. Particularly, the 10-15 year old dodonea viscosa hedge that were in its vicinity or planted in the same row; they have also died recently.

I am unable to understand the issue as I checked roots of dead dodonea viscosa, they were dry/rotten without any visible pests.

The climate was unusually hot this year and then we had lot of rain in North India where I live.

Please advise what can I do to save this tree and neighbouring plants.

This week I trimmed down the branches to cut all dead branches and dying branches. Last picture shows what’s left of branches now. It is still drying from leaves, shoots.