Wireless sensor networks usually operate under light traffic loads. However, when an event is detected, a large volume of data may be generated and delivered to the sink. The demand for simultaneous data transmission may cause severe channel collision and thus decrease communication throughput in contention-based medium access control (MAC) protocols. In this paper, we introduce a novel receiver-centric data transmission paradigm, which takes advantage of the tree structure that is naturally formed in data collection of a sensor network to assist scheduling of channel access. On the tree structure, a receiver is able to coordinate its multiple senders' channel access so as to reduce channel contention and consequently improve communication throughput. The protocol seamlessly integrates scheduling with contention-based medium access control. In addition, to ensure reliable data transmission, we propose a sequence-based lost packet recovery scheme in a hop-by-hop recovery pattern, which could further improve communication throughput by reducing control overhead. We present the performance of our receiver-centric MAC protocol through measurements of an implementation in TinyOS on TelosB motes and extend the evaluation through ns-2 simulations. Compared with B-MAC and RI-MAC, we show the benefits of improving throughput and fairness through receiver-centric scheduling under heavy traffic loads.