Traffic grooming is being considered as a key functionality of WDM networks, in which, multiple low speed traffic requests are groomed into a single high capacity wavelength channel. In this work, multicast traffic grooming problem is addressed to maximize the bandwidth utilization for a set of sessions in an optical WDM mesh topology. We propose a heuristic approach called Prioritized Multicast Traffic Grooming (PMTG) for constructing multicast tree and a first fit algorithm for wavelength assignment. After successful grooming of multicast requests, PMTG algorithm have successfully reduced the maximum number of wavelengths required in a link at the same time bandwidth utilization has greatly improved. We have simulated the heuristic approach PMTG with different network topologies and compared the performance with Multicast Traffic Grooming with Shortest Path (MTG-SP) algorithm. The simulation results show that the proposed heuristic algorithm produces better result than MTG-SP based algorithm.