The RCEP is an economic bloc mostly consisting of Asian and Australasian countries who trade with each other under duty-free conditions, expanding the member country products to larger, more stable markets. The pre-requisite of accessing larger markets is that you have to open your market up for other members as well.
The BRIC (Brazil, Russia, India, China) is an economic bloc mostly consisting of the four countries who are currently looking to create alternatives for the dollar economy, so to aid various other countries within its umbrella to shift away from dependence on the dollar. Recently, BRICs endorsed Saudi Arabia, Iran, United Arab Emirates, Egypt, Ethiopia and Argentina to join the bloc.
Bangladesh wanted and lobbied to join both.