no country can ban bitcoin. the only way they could do is by banning internet which is not practical today's world, so what people say countries banning bitcoin is the process of discouraging (or reducing chances of) people buying bitcoin by giving official announcements, banning exchanges, etc. but in reality no one can really ban bitcoin, but developing countries like Bangladesh sometimes tend to try to reduce use of digital currencies like bitcoin due to fear of loosing tax (by money laundering etc.)