Insert selected records from Nested (Child) GridView to Database in ASP.Net

I already made it! ^_^

this is my code

protected void addchk_modalpopup_save_Click(object sender, ImageClickEventArgs e)
    {
        CheckBox chk = (sender as CheckBox);
        int x = 0;
        DataTable dt = new DataTable();
        foreach (GridViewRow row in GridView1.Rows)
        {
            if (row.RowType == DataControlRowType.DataRow)
            {
                CheckBox chkRow = (row.Cells[0].FindControl("chkAll") as CheckBox);
                if (chkRow.Checked)
                {

                    GridView GridView2 = (GridView)row.FindControl("GridView2");

                    for (int i = 0; i < GridView2.Rows.Count; i++)
                    {
                        CheckBox cbx = (CheckBox)GridView2.Rows[i].FindControl("ck2");
                        if (cbx.Checked)
                        {
                            x++;
                            //string firstColumnValue = GridView1.Rows[i].Cells[0].Text;
                        }
                    }

                    foreach (GridViewRow row2 in GridView2.Rows)
                    {
                        if (row2.RowType == DataControlRowType.DataRow)
                        {
                            bool isChecked = row2.Cells[0].Controls.OfType<CheckBox>().FirstOrDefault().Checked;
                            if (isChecked == true)
                            {
                                string checklist = row.Cells[1].Text;
                                string activity = row2.Cells[1].Text;
                                connection();
                                amicassaCon.Open();
                                SqlCommand insert = new SqlCommand("INSERT INTO checklist_activity (contract_num,milestone,checklist,activity) VALUES('" + contract_no.Text + "','" + milestonedrpdwnlist.SelectedValue + "','" + checklist + "','" + activity + "')", amicassaCon);
                                SqlDataReader dr = insert.ExecuteReader();
                                dr.Close();
                                amicassaCon.Close();
                            }
                        }
                    }        
                }
            }
        }
    }

 this is my markup

<asp:GridView ID="GridView1" runat="server" RowStyle-VerticalAlign="Top" AutoGenerateColumns="False" CellPadding="4" OnRowDataBound="OnRowDataBound" DataKeyNames="checklist" Width="100%" ForeColor="#333333" GridLines="None">
<AlternatingRowStyle VerticalAlign="Top" BackColor="White"></AlternatingRowStyle>
                    <Columns>
                        
                        <asp:TemplateField ItemStyle-Width=".01px" ItemStyle-Height="1">
                            <ItemTemplate>
                                <asp:CheckBox ID="chkAll" AutoPostBack="true" OnCheckedChanged="OnCheckedChanged" runat="server" Font-Size="XX-Small" />
                            </ItemTemplate>
                            <ItemStyle Height="5px" Width="5px"/>
                        </asp:TemplateField>
                        
                        <asp:BoundField DataField="checklist" HeaderText="Checklist" />
                        <asp:TemplateField HeaderText="Activity">
                            <ItemTemplate>
                                <asp:GridView ID="GridView2" RowStyle-VerticalAlign="Top" ShowHeader="false" RowStyle-HorizontalAlign="left"  runat="server" Width="100%" AutoGenerateColumns="False" CellPadding="4" ForeColor="#333333" GridLines="None" >
                                    <AlternatingRowStyle BackColor="White" HorizontalAlign="Left" VerticalAlign="Top" />
                                    <Columns>
                                        <asp:TemplateField ItemStyle-Width=".01px" ItemStyle-Height="1">
                            <ItemTemplate >
                                <asp:CheckBox ID="ck2" runat="server" Width="3px" Height="3px"/>
                            </ItemTemplate>
                                            <ItemStyle Width="0px" />
                        </asp:TemplateField>
                                    <asp:BoundField DataField="activity" ItemStyle-Width="90%">
                                        <ItemStyle Width="90%" />
                                        </asp:BoundField>
                                    </Columns>
                                    <EditRowStyle BackColor="#7C6F57" />
                                    <FooterStyle BackColor="#1C5E55" ForeColor="White" Font-Bold="True" />
                                    <HeaderStyle BackColor="#015e46" Font-Bold="True" ForeColor="White" />
                                    <PagerStyle ForeColor="White" HorizontalAlign="Center" BackColor="#666666" />
                                    <RowStyle BackColor="#E3EAEB" />
                                    <SelectedRowStyle BackColor="#C5BBAF" Font-Bold="True" ForeColor="#333333" />
                                    <SortedAscendingCellStyle BackColor="#F8FAFA" />
                                    <SortedAscendingHeaderStyle BackColor="#246B61" />
                                    <SortedDescendingCellStyle BackColor="#D4DFE1" />
                                    <SortedDescendingHeaderStyle BackColor="#15524A" />
                                </asp:GridView>
                            </ItemTemplate>
                        </asp:TemplateField>
                    </Columns>
                    <EditRowStyle BackColor="#7C6F57" />
                    <FooterStyle BackColor="#1C5E55" ForeColor="White" Font-Bold="True" />
                    <HeaderStyle BackColor="#015e46" Font-Bold="True" ForeColor="White" />
                    <PagerStyle ForeColor="White" HorizontalAlign="Center" BackColor="#666666" />
                    <RowStyle BackColor="#E3EAEB" />
                    <SelectedRowStyle BackColor="#C5BBAF" Font-Bold="True" ForeColor="#333333" />
                    <SortedAscendingCellStyle BackColor="#F8FAFA" />
                    <SortedAscendingHeaderStyle BackColor="#246B61" />
                    <SortedDescendingCellStyle BackColor="#D4DFE1" />
                    <SortedDescendingHeaderStyle BackColor="#15524A" />
                </asp:GridView>