colspan gridview rows

I have added rows into gridview. There are 20 columns in gridview. How can i do a colspan-like feature in gridview which could show me 2-3 rows under 2-3 columns and remaining as a colspan.

Basically i wish to implement colspan in gridview on the rows of the gridview.

hence my present gv is like ;

Col 1 Col 2 Col 3 Col 4 ...... Col 20

Cell1 Cell2 Cell3 Cell 4 ...... Cell 20 (For Rows # 1)

I wish to have something like

Col 1 Col 2 Col 3 Col 4 ...... Col 20

    Cell1      Cell2    ...... Cell 20   (For Rows # 1)

Let me know for any query.

Thanks