<table>
  <tr>
     <td>
        <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
     </td>   
  </tr>
  <tr>
    <td>
      	<asp:Button ID="Button1" runat="server" onclick="Button1_Click" Text="Submit" />
    </td>   
  </tr>
  <tr>
    <td>
       <asp:GridView ID="GridView1" runat="server">
       </asp:GridView>
    </td>   
  </tr>  
</table>

if (!Page.IsPostBack)
{
    BindGrid();
}

public void BindDropDown()
{
  if (!File.Exists("D:\\First2008Sample\\Master.xml"))
  {
      DataSet oDs = new DataSet();
      oDs.ReadXml("D:\\First2008Sample\\Master.xml");
      GridView1.DataSource = oDs;
      GridView1.DataBind();
  }
}
  
protected void Button1_Click(object sender, EventArgs e)
{
        if(Button1.Text == "Submit")
        {
            if (!File.Exists("D:\\First2008Sample\\Master.xml"))
            {
                XmlDocument oXmlDoc = new XmlDocument();
                oXmlDoc.AppendChild(oXmlDoc.CreateXmlDeclaration("1.0", null, "yes"));
                
                
                //......Creating Parent Locations Tag.
                
                XmlElement oXmlPar = oXmlDoc.CreateElement("Locations");
                
                //......Creating Child Nodes Under Parent Node.
                
                XmlElement oXmlEleLoc = oXmlDoc.CreateElement("Location");
                
                //......Creating Attributes In Child Node.
                
                XmlAttribute oXmlAttrId = oXmlDoc.CreateAttribute("Id");
                oXmlAttrId.Value = "1";
                
                //......Appending Attributes To The Child Node.
                
                oXmlEleLoc.Attributes.Append(oXmlAttrId);
                
                //......Creating Elements To The Child Node.
                
                XmlElement oXmlLocId = oXmlDoc.CreateElement("Location_Id");
                XmlElement oXmlLocText = oXmlDoc.CreateElement("Location_Text");
                XmlElement oXmlLocStatus = oXmlDoc.CreateElement("Status");
                
                //......Assigning Values To Elements Under The Child Node.
                
                oXmlLocId.AppendChild(oXmlDoc.CreateTextNode("Loc_1"));
                oXmlLocText.AppendChild(oXmlDoc.CreateTextNode(TextBox1.Text));
                oXmlLocStatus.AppendChild(oXmlDoc.CreateTextNode("U"));
                
                //......Appending Elements To Child Nodes.
                
                oXmlEleLoc.AppendChild(oXmlLocId);
                oXmlEleLoc.AppendChild(oXmlLocText);
                oXmlEleLoc.AppendChild(oXmlLocStatus);
                
                //......Appending Child Nodes To Parent Node.
                
                oXmlPar.AppendChild(oXmlEleLoc);
                oXmlDoc.AppendChild(oXmlPar);

                oXmlDoc.Save("D:\\First2008Sample\\Master.xml");

                Response.Write("< script language='javascript' >alert('Location has been created successfully.'); location.href='CreateXML.aspx';< /script >");
            }
            else
            {
                XmlDocument oXmlDoc = new XmlDocument();
                oXmlDoc.Load("D:\\First2008Sample\\Master.xml");
                
                //......Verifying That Location Is Already Existing In The XML File.
                
                XmlNode oXmlLoc = oXmlDoc.SelectSingleNode("Locations/Location[Location_Text='" + TextBox1.Text + "']");
                
                //......Returns Null If It Doesnot Exists.
                
                if (oXmlLoc == null)
                {
                    int iNodeCnt = oXmlDoc.DocumentElement.ChildNodes.Count;
                    iNodeCnt++;
                    
                    //......Creating Child Nodes Under Parent Node.
		    
                    XmlElement oXmlEleLoc = oXmlDoc.CreateElement("Location");
                    
                    //......Creating Attributes In Child Node.
                    
                    XmlAttribute oXmlAttrId = oXmlDoc.CreateAttribute("Id");
                                        
                    oXmlAttrId.Value = iNodeCnt.ToString();
                    oXmlEleLoc.Attributes.Append(oXmlAttrId);
                    XmlElement oXmlLocId = oXmlDoc.CreateElement("Location_Id");
                    XmlElement oXmlLocText = oXmlDoc.CreateElement("Location_Text");
                    XmlElement oXmlLocStatus = oXmlDoc.CreateElement("Status");

                    oXmlLocId.AppendChild(oXmlDoc.CreateTextNode("Loc_" + iNodeCnt.ToString()));
                    oXmlLocText.AppendChild(oXmlDoc.CreateTextNode(TextBox1.Text));
                    oXmlLocStatus.AppendChild(oXmlDoc.CreateTextNode("U"));

                    oXmlEleLoc.AppendChild(oXmlLocId);
                    oXmlEleLoc.AppendChild(oXmlLocText);
                    oXmlEleLoc.AppendChild(oXmlLocStatus);

                    oXmlDoc.DocumentElement.AppendChild(oXmlEleLoc);

                    oXmlDoc.Save("D:\\First2008Sample\\Master.xml");
                    Response.Write("< script language='javascript' >alert('Location has been created successfully.'); location.href='CreateXML.aspx';< /script >");
                }
                else
                {
                    Response.Write("< script language='javascript'>alert('Location already exists.');< /script >");
                    return;
                }
            }
        }        
}

<?xml version="1.0" standalone="yes"?>
<Locations>
  <Location Id="1">
    <Location_Id>Loc_1</Location_Id>
    <Location_Text>a</Location_Text>
    <Status>U</Status>
  </Location>
  <Location Id="2">
    <Location_Id>Loc_2</Location_Id>
    <Location_Text>b</Location_Text>
    <Status>U</Status>
  </Location>
</Locations>