Appending Data to xml file

Hello Experts,

I am attempting to append a new data to an xml file, where as my xml file contains root element "$current month" and when user add details at the first get saved into xml file as...

<?xml version="1.0" encoding="utf-8"?>
<March>
  <SrNo>1</SrNo>
  <Title>test1</Title>
  <Amount>559012</Amount>
  <Status>Paid</Status>
</March>

With below coding as ....

Public Class Expense_Details
    Private Sub Expense_Details_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        ComboBox1.Items.Add("Paid")
        ComboBox1.Items.Add("UnPaid")
        'Display current month
        Dim currentmonth As String
        currentmonth = String.Format("{0:MMMM}", DateTime.Now).ToString()
        Label3.Text = currentmonth
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim srNo As Integer = TextBox1.Text
        Dim Title As String = TextBox2.Text
        Dim Amt As Integer = TextBox3.Text
        Dim Status As String = ComboBox1.SelectedItem
        Dim mywriter As XmlWriter = XmlWriter.Create(Application.StartupPath & "\XmlTest.xml")
        mywriter.WriteStartDocument()
        mywriter.WriteStartElement(String.Format("{0:MMMM}", DateTime.Now).ToString())
        mywriter.WriteEndElement()
        mywriter.Flush()
        mywriter.Close()
        Dim xmldoc As XmlDocument = New XmlDocument
        xmldoc.Load(Application.StartupPath & "\XmlTest.xml")
        Dim root As XmlElement = xmldoc.SelectSingleNode(String.Format("{0:MMMM}", DateTime.Now).ToString())
        Dim element1 As XmlElement = xmldoc.CreateElement("SrNo")
        Dim value As XmlText = xmldoc.CreateTextNode(srNo)
        element1.AppendChild(value)
        root.AppendChild(element1)
        Dim element2 As XmlElement = xmldoc.CreateElement("Title")
        Dim value2 As XmlText = xmldoc.CreateTextNode(Title)
        element2.AppendChild(value2)
        root.AppendChild(element2)
        Dim element3 As XmlElement = xmldoc.CreateElement("Amount")
        Dim value3 As XmlText = xmldoc.CreateTextNode(Amt)
        element3.AppendChild(value3)
        root.AppendChild(element3)
        Dim element4 As XmlElement = xmldoc.CreateElement("Status")
        Dim value4 As XmlText = xmldoc.CreateTextNode(Status)
        element4.AppendChild(value4)
        root.AppendChild(element4)
        xmldoc.Save(Application.StartupPath & "\XmlTest.xml")
    End Sub
    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        Application.Exit()
    End Sub
End Class

Can you please help me with an button next click, the user enters data which should get added to existing data like...

<?xml version="1.0" encoding="utf-8"?>
<March>
  <SrNo>1</SrNo>
  <Title>test1</Title>
  <Amount>559012</Amount>
  <Status>Paid</Status>
  <SrNo>2</SrNo>
  <Title>useradded</Title>
  <Amount>5590</Amount>
  <Status>UnPaid</Status>
</March>

Is there any references or examples for the same.

Thanks,
Shailesh