Yes, if you go with the Mostbet download in Bangladesh option 

https://mostbet-app-download.com/en_bd/mostbet-bd/ you actually get a welcome bonus right after the first deposit. The app itself prompts you with 100 free spins or a matched bonus depending on what you choose. I liked that it works instantly after installation. The app also keeps all features from the desktop version, so you’re not missing anything by using mobile. It makes sense to install it directly because you get both the convenience of betting on the go and the extra rewards at the start.