In the application based WSN environment, energy and bandwidth of the sensor are valuable resources and need to utilize efficiently. Data aggregation at the sink by individual node causes flooding of the data which results in maximum energy consumption. To minimize this problem we propose and evaluate the group based data aggregation method, where grouping of nodes based on available data and correlation in the intra-cluster and grouping of cluster heads at the network level help to reduce the energy consumption. In addition, proposed method uses additive and divisible data aggregation function at cluster head (CH) as in-network processing to reduce energy consumption. Cluster head transmits aggregated information to remote sink and cluster head nodes transmit data to CH. Simulation result shows, proposed algorithm provides an improvement of 14.94% in energy consumption as compared with primary cluster based protocol LEACH which uses only one CH, it also improves the network stability.