In this paper, we analyse a queueing system with a second optional service channel under bi-level control policy and server’s single vacation. There is a single server who provides the first essential service to all arriving customers. As soon as the first service of a customer is complete, then with probability r , the customer may opt for the second service in which case the second service will immediately commence, or else with probability (1 – r ) he may opt to leave the system, so that another customer at the head of the queue (if any) is taken up for his first essential service. The server operates an ( m , N ) policy with an early setup and takes a single vacation whenever the system becomes empty. For this model, the stationary probability generating function of the queue length distribution is obtained through supplementary variable technique and a decomposition property is discussed. The expected length of the cycle, various performance measures and the optimal values of thresholds m and N which minimise the total expected operating cost are also calculated.