Why is that in sites like Investing.com the Volumes Chart or underlay is available even for NIFTY50 and Banknifty and at times when i have to look for the volumes since it forms a part of my strategy to trade them i have to look for the same in there. Since the volumes are available in the bhav copy would request you to please add them in the Indices charts also wherever available , hope this should not require much of change from your side