Hi Shivinder,
Thanks for your interest on Syncfusion products.
You can add your custom menu items to the default context menu by initializing ChartArea.ContextMenuType = DefaultWithCustom, and adding new menu items to the ChartArea.CustomContextMenuItems.
Please find the attached sample, which demonstrates how to add custom context menu items to the default context menu.
Regards,
Abdul Rahman
Sample_2d786ec6.zip