I found the following post from the blog, Third World View. The 1972 constitution names Bangladesh the land of Bengalis with no mention of traditional or indigenous peoples. These indigenous communities want to be recognized as such, but government officials feel that rewriting the constitution to include their indigenous status may lead to the idea that 'Bengalis' are "invaders" or "intruders" to Bangladesh. The ethnic minorities who mainly reside in the hill tracts of Bangladesh have been subject to human rights abuses for many years. This classification has great importance in the eyes of the indigenous peoples in terms of their cultural identity, rights and status in Bangladesh. Read their history and their words (in English and Bangla) in the original post "Bangladesh: Indigenous or Not Indigenous, That is the Question" here.