How to access the Nested Gridview id?

Hello,
I am using Northwind DB and i have a gridview name gvwSelf and a Nested gridview gvwNested. What i do is i filter my dataset based on the
categoryName and accordingly display the result in the Gridview. Filteration works perfect however, i am unable to access my gvwNested...Pl..find my sample code below and please help me to find where am i going wrong..:(

<asp:GridView ID="gvwSelf" runat="server" AutoGenerateColumns="False" DataKeyNames="CategoryID">
   
        <Columns>
        
            <asp:BoundField DataField="CategoryName" HeaderText="Name" />
            <asp:BoundField DataField="Description" HeaderText="Description" />
            <asp:TemplateField>
                <ItemTemplate >
                
                    <asp:GridView ID="gvwNested" runat="server" AutoGenerateColumns="False">
                        <Columns>
                            <asp:BoundField DataField="CategoryID" HeaderText="ID" />
                            <asp:BoundField DataField="CategoryName" HeaderText="Name" />
                            <asp:BoundField DataField="Discription" HeaderText="Description" />
                        </Columns>
                    </asp:GridView>
                </ItemTemplate>
            </asp:TemplateField>
        </Columns>
        </asp:GridView>

IN .CS Page:

private void BindGridView()
           
        {
            string str = "";
            SqlConnection con = new SqlConnection(str);
            string cmd = "Select * from categories";
            DataSet ds = new DataSet();
            SqlDataAdapter da = new SqlDataAdapter(cmd,str);
            da.Fill(ds);
            DataTable tblData = ds.Tables[0];
            tblData.DefaultView.RowFilter = "CategoryName = 'Beverages'";
            gvwSelf.DataSource = tblData;
            gvwSelf.DataBind();

            GridView gvwnested = new GridView();
            gvwnested = (GridView)gvwSelf.FindControl("gvwNested");    // I get gvwNested as NULL             DataTable tblNested = ds.Tables[0];
            tblNested.DefaultView.RowFilter = "CategoryName = 'Condiments'";
            gvwnested.DataSource = tblNested; // Object Reference Error             gvwnested.DataBind();


        }

Also, i want to know how to display my gvwNested below my gvwSelf...also i want display header to each of them so that the sections are diffrentiated...

Please help

Best Regards,
Rohan Laghate