P.S. The photographs have been taken through different seasons.
Reproduced below is his feedback:
This feature I have observed in Nana Tree [Lagerstroemia laceolata] also belonging to the same family.
In fact there is a very good such specimen of Nana with these sorts of
spines on the Rajmachi trail.
When I had inquired with a local person about this odd characteristic he had
told me that if while the tree is young, its main trunk portion is injured
or cut for any reason and then when it starts growing again this kind of
change is seen.
For the record my tree suffered no such injury/insult.