How to generate child rows inside gridview

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C#

ASP.NET

SQL-Server

Gridview

Created gridview in asp.net c#.Adding each row with button click .now i want to create child rows for particular row. like 1.1,1.2...while clicking add button (in each row).how to do it?

What I have tried:

Front end

 <asp:gridview ID="Gridview1" runat="server" ShowFooter="true" 
        AutoGenerateColumns="false" >
        <Columns>
        <asp:BoundField DataField="RowNumber" HeaderText="Row Number" />
        <asp:TemplateField HeaderText="Col 1">
            <ItemTemplate>
                <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="Col 2">
            <ItemTemplate>
                <asp:TextBox ID="TextBox2" runat="server"></asp:TextBox>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="Col 3">
            <ItemTemplate>
                 <asp:TextBox ID="TextBox3" runat="server"></asp:TextBox>
            </ItemTemplate>
             </asp:TemplateField>
                <asp:TemplateField >
            <ItemTemplate>
                 <asp:LinkButton ID="Link1" runat="server">Add</asp:LinkButton>
            </ItemTemplate>
            
            
            <FooterStyle HorizontalAlign="Right" />
            <FooterTemplate>
             <asp:Button ID="ButtonAdd" runat="server" Text="Add New Row" OnClick="ButtonAdd_Click" />
            </FooterTemplate>
        </asp:TemplateField>
        </Columns>
</asp:gridview>

code behind

private void AddNewRowToGrid()
        {
            int rowIndex = 0;

            if (ViewState["CurrentTable"] != null)
            {
                DataTable dtCurrentTable = (DataTable)ViewState["CurrentTable"];
                DataRow drCurrentRow = null;
                if (dtCurrentTable.Rows.Count > 0)
                {
                    for (int i = 1; i <= dtCurrentTable.Rows.Count; i++)
                    {
                        //extract the TextBox values
                        TextBox box1 = (TextBox)Gridview1.Rows[rowIndex].Cells[1].FindControl("TextBox1");
                        TextBox box2 = (TextBox)Gridview1.Rows[rowIndex].Cells[2].FindControl("TextBox2");
                        TextBox box3 = (TextBox)Gridview1.Rows[rowIndex].Cells[3].FindControl("TextBox3");

                        drCurrentRow = dtCurrentTable.NewRow();
                        drCurrentRow["RowNumber"] = i + 1;

                        dtCurrentTable.Rows[i - 1]["Column1"] = box1.Text;
                        dtCurrentTable.Rows[i - 1]["Column2"] = box2.Text;
                        dtCurrentTable.Rows[i - 1]["Column3"] = box3.Text;

                        rowIndex++;
                    }
                    dtCurrentTable.Rows.Add(drCurrentRow);
                    ViewState["CurrentTable"] = dtCurrentTable;

                    Gridview1.DataSource = dtCurrentTable;
                    Gridview1.DataBind();
                }
            }
            else
            {
                Response.Write("ViewState is null");
            }
            SetPreviousData();
        }