We investigate the impact of massive MIMO on the uplink transmission design for a heterogeneous network (HetNet) where multiple users communicate with a macro-cell base station (MCBS) through multiple small-cell BSs (SCBSs). We develop a new scheme in which the SCBSs deploy decode-forward (DF) relaying, multi-layer binning, and time division transmission, where the number of binning layers (resp. time slots) is equal to the number of SCBSs (resp. users). The MCBS separately and sequentially decodes the binning indices and each user's message that belongs to those indices. The proposed scheme is simpler than schemes with common transmission of all users' messages by each SCBS and joint decoding at the MCBS: 1) the codebook size and the decoding complexity increase linearly with the number of users instead of exponentially, 2) every transmission-decoding step is similar to the conventional point-to-point communication, and 3) the same set of time slot durations at all SCBSs is sufficient to achieve the maximum rate. Despite its simplicity, the proposed scheme is effective since it achieves the same rate performance of more complex schemes with joint decoding.