A fundamental challenge in the design of Wireless Sensor Networks (WSNs) is to maximize their lifetime especially because they have a limited and non- exchangeable energy supply. One of the most important methods to prolong the lifetime of a WSN is data ag- gregation. Indeed, data aggregation reduces the number of broadcasts, hence collisions and energy consumption. Many methods has been proposed in the literatures to organize the network for data aggregation like cluster- ing which has been proved to provide the best perfor- mance in term of energy saving, aggregation gain and packet delivery accuracy, or structure-free which has been proved to perform better than a structure-based data gathering. To benefit all the advantages of these two approaches, we propose a hybrid method that com- bines multilevel structure-based approaches for time- constrained wireless sensor networks. Simulation results show that our proposed method can improve aggrega- tion gain and energy consumption.