To avoid collisions in cluster tree routing and improve the network performance in IEEE 802.15.4 sensor networks, effective scheduling mechanisms need to be developed. In this study, a multiple cluster tree routing technique along with scheduling, for collision avoidance is proposed. Multiple cluster trees are designed in which the Cluster Heads (CH) are responsible for scheduling. Each CH schedules it member nodes with appropriate time slot considering the amount of data to be transmitted with regard to the time interval. Apart from this, cluster tree rejoining procedure is designed in which suitable parents are selected based on link quality indicator. Through simulation results, the proficiency of our technique is proved.