Help me identify this insect from Bangladesh
This is actually the flying adult of a scale insect (superfamily Coccoidea). Specifically, this appears to be some species of the genus Drosicha.

Here is a picture resembling your specimen:



 Source: John Horstman

And another from Vietnam that looks very similar:



 Source: Dan Doucette

I can only find info on a closely related species, Drosicha corpulenta, and here's a tree of related species. 

Scalenet provides numerous keys and references that could be useful for positively IDing this specimen.

I will keep searching for more details, but this might be the best you get without asking a scale insect expert.