Bangladesh does not have an officially designated national vegetable. Nations often have national symbols such as flags, animals, and flowers, but not all of them have a national vegetable. I recommend checking more recent sources to see if Bangladesh has officially declared a national vegetable.
However, is it very likely that soon, eggplant (Called Brinjal in Bangladesh) will become the national vegetable of this country.
I hope this helped!
~~~Harsha~~~