Mahesh Khali is the only hilly island in Bangladesh. Combined with Kutub Dia, another island smaller than Mahesh Khali forms the constituency known as Cox's Bazar-2 in Bangladesh Parliament. It is an upazillah(sub-district) under Cox's Bazar.
Map of Maheskhali Island, Bangladesh
Maheshkhali Island is the main island of Maheshkhali Upazila, in the Cox's Bazar District of Bangladesh.
References
Maheshkhali Island Wikipedia(Text) CC BY-SA