I love gardening ( fruit trees ) but from my experience of buying plants I have seen that in Bangladesh lots of fruit species and varieties are not available yet . Collection of different species and varieties of fruit plants is a part of my hobby . So I was thinking if I ever visit India then I'll collect some rare fruit trees and bring them here . But I am not sure about the allowance of bringing live plants from India to BANGLADESH.
I would agree with the commenter above (you should do research about Bangladesh's import rules for plants, as well as common diseases) and add that it all comes down to the declaration and inspection at your port of arrival (airport/port/train station).
Even with your best research there's a very real chance that Customs may decide to seize your plants and destroy them, if they contravene some obscure regulation you did not happen to research or if the customs agent has a poor understanding of the actual regulations. Therefore, I would caution you against buying a bunch of exotic plants and spending a lot of money, only for all of it to be seized.
If plant collecting is a hobby of yours, you should find like-minded individuals in your community who might know more about why certain species of plants have not yet made it to Bangladesh (are they invasive, poorly suited to the climate, etc).