It's a Begonia, but there are plenty of species in the genus!

The plant is Begonia sp. of Begoniaceae family. There are eight species of Begonia found in Bangladesh. Please have a look at this link.

https://www.researchgate.net/publication/267296208_Distribution_Patterns_of_Begonia_species_in_the_Nepal_Himalaya

Article Distribution Patterns of Begonia species in the Nepal Himalaya

 Begoniaceae is quite interesting genus, and difficult to identify. Base on small plant charater, they are easy overlooked in field survey, so many new species of Begonia had found in recent years. 

yes. it seem to me quite difficult to this begonia sp. i hv to look for a begoniaceae expert:) 

The plant is Begonia sp. of Begoniaceae family but species is difficult to pin point.