Insert,Update and Delete in XML file with xmldoc nad xmlelement

How to Read XML and insert a node in xml file
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'Insert in xml if not available.....
Dim strXmlPath As String = Server.MapPath("~/App_Data/reminder.xml")
Dim xmlDoc As New XmlDocument()
xmlDoc.Load(strXmlPath)
Dim nodeList As XmlNodeList = xmlDoc.SelectNodes("/reminder_list/reminder[@ID='" & Session("UserName").ToString().ToLower() & "']")

Dim xmlNamespace As String = [String].Empty
Dim parentNode As XmlElement = xmlDoc.CreateElement("reminder", xmlNamespace)
xmlDoc.DocumentElement.AppendChild(parentNode)
Dim t As XmlNode = xmlDoc.SelectSingleNode("/reminder_list/reminder[@rem_id='" & objReminder.ReminderId & "' and @ID='" & Session("UserName").ToString().ToLower() & "' and @subject='" & txtSuject.Text.Trim & "']")
If Convert.ToString(t) <> "" Then
t.ParentNode.RemoveChild(t)
parentNode.SetAttribute("end_date", strRemDateTime)
parentNode.SetAttribute("ID", Session("UserName").ToString().ToLower())
parentNode.SetAttribute("rem_id", hidremid.Value)
parentNode.SetAttribute("subject", txtSuject.Text.Trim)
parentNode.SetAttribute("start_date", Date.Now)
parentNode.SetAttribute("reminder", txtmsg.Text)
parentNode.SetAttribute("flag", 1)
xmlDoc.Save(strXmlPath)
Else
parentNode.SetAttribute("end_date", strRemDateTime)
parentNode.SetAttribute("ID", Session("UserName").ToString().ToLower())
parentNode.SetAttribute("rem_id", hidremid.Value)
parentNode.SetAttribute("subject", txtSuject.Text.Trim)
parentNode.SetAttribute("start_date", Date.Now)
parentNode.SetAttribute("reminder", txtmsg.Text)
parentNode.SetAttribute("flag", 1)
xmlDoc.Save(strXmlPath)
End If