Some quotes from cricinfo report regarding 20-man training squard.
About Alok's ommision
"One notable omission is Alok Kapali, Bangladesh's underachieving allrounder"
About Shahadat & Shahriar
"they have a degree of experience despite their tender years. "
About Inclusion of Tushar and Anwar
"The batsman, Tushar Imran and the seam bowler, Anwar Hossain Munir, have been recalled after consistent performances for the Bangladesh A team and the BCB XI respectively"
About Inclusion of ChaCha
"the former captain and allrounder, Khaled Mahmud, whose form in Bangladesh's domestic competitions has been irresistible."
cricinfo