Bangladesh is a Muslim-majority nation (~91% Sunni Islam, 2022 census). The constitution designates Islam as the state religion while guaranteeing freedom of worship.
There is no single "main god" in a polytheistic sense. For the overwhelming majority, the one God is Allah (Arabic for "The God"), worshiped per Islamic theology—tawhid (oneness), no partners, no idols.
Article 2A: "The state religion of the Republic is Islam." Article 41: "Subject to law, public order and morality, every citizen has the right to profess, practice or propagate any religion."