just use Gridview control within Gridview
<asp:GridView ID="GridView1" runat="server" CellPadding="4" ><Columns>
<asp:TemplateField>
<ItemTemplate>
<table>
<tr>
<td>
</table> <asp:Label ID="catagory" runat="server" Text=""></asp:Label>
</td>
<td>
<asp:GridView ID="GridView2" runat="server">
<Columns>
<asp:TemplateField>
<ItemTemplate>
<asp:Label ID="subcatagory" runat="server" Text=""></asp:Label>
</ItemTemplate>
</asp:TemplateField>
</Columns>
</asp:GridView>
</td>
</tr>
</ItemTemplate>
</asp:TemplateField>
</Columns>
</asp:GridView>
Bind the Subcatagory values at Gridview1 Row Databound..
Got It...