Wireless Sensor Networks (WSN) is turning out as a well known because it has vast number of applications in the area of research. They have various applications like smart homes, agricultural monitoring, weather forecasting, etc. Moreover, WSN be susceptible to many attacks. Within these networks nodes are randomly distributed in search field. This is done to observe both physical as well as environmental conditions. However, sensor nodes in WSN¿s are battery aware, so, may be lifeless, within a definite time. Battery of sensors cannot be replaced not even regenerate. Therefore, energy efficiency has become the most important concern in WSN¿s. The energy of WSN¿s can be improved by using clustering as well as tree-based data aggregation protocols.