Broadcast and convergecast are two fundamental operations which often happen simultaneously in a wireless sensor network. Previous works have addressed energy-efficient, low-latency scheduling but they only try to optimize the traffic in one direction (broadcast or convergecast). This work defines a low-latency two-way beacon scheduling (LTBS) problem for ZigBee tree-based networks, where beacons stand for timing for nodes to deliver broadcast and convergecast traffics. We formulate the problem as a slot assignment problem where each node needs to obtain slots for upstream and downstream transmissions while avoiding interferences. We propose two efficient slot assignment algorithms based on the concept of sequencing nodes’ slots to facilitate two-way traffics. We show the advantages of these schemes through extensive simulations. The results indicate that these two slot assignment algorithms can indeed achieve low-latency in ZigBee networks.