Serial number for GridView Rows

Hi everybody,
I have a gridview in my gridview i display the data whatever i want. That's totally completed except small point. I want to display serial numbers at first column. I know how to give serial number but i need in below format. Can any one help me out of this.
SNo Material Grade 1 RCC M30 1.a M50 1.c M70 2 FormWork column 2.a Plates Can any one give me some suggestion to achieve my serial number in above format.
 
Thanks in Advance
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