Wireless Sensor Networks (WSN) are set of thousands or more micro sensor nodes that one of the most important constraints of them is their limited energy. Since these nodes have very small dimensions, so their needed energy is provided by small and limited energy batteries. Therefore, the problem of energy reduction will be one of the biggest challenges in these networks. In this paper, we will propose a new cluster-based method that can reduce the average energy consumption in each round using a new method for data packet transmission to BS. In this method, all normal nodes and all cluster heads (CHs) use a tree structure for transmit their data packets toward the cluster heads and BS respectively. In fact, the energy consumption is reduced in contrast to LEACH through the following modifications. 1) minimization of hop lengths which are necessary to transmission of data packets inside the clusters 2) via continuously data aggregation in and out of the clusters 3) the selection of the nearest cluster head to the BS for transmission of final data packet toward the BS in each round. Simulation results show that the new algorithm decreases the average energy consumption of sensor network in contrast to LEACH.