Insert a new entry in XML

I have an XML below like this and I want to add in another entry to it:

<?xml version="1.0" encoding="utf-8"?>
<CampaignRewardsVoucher>
  <VoucherCode>Vouch001</VoucherCode>
  <Quantity>3</Quantity>
</CampaignRewardsVoucher>

I have the above xml but I want to add Vouch002 after Vouch001:

  <VoucherCode>Vouch002</VoucherCode>
  <Quantity>3</Quantity>
  </CampaignRewardsVoucher>

I have the code below which checks if an input is a duplicate and update accordingly, if not I want to create a new Vouch002 entry, please advice, thanks:

'Create XmlWriterSettings
        Dim settings As XmlWriterSettings = New XmlWriterSettings()
        settings.Indent = True

        If (Not File.Exists("D:\CampaignRewardsVoucher.xml")) Then

            'Create XmlWriter
            Using writer As XmlWriter = XmlWriter.Create("D:\CampaignRewardsVoucher.xml", settings)

                'Begin write
                writer.WriteStartDocument()
                writer.WriteStartElement("CampaignRewardsVoucher")
                writer.WriteElementString("VoucherCode", DropDownList1.SelectedValue)
                writer.WriteEle开发者_如何学PythonmentString("Quantity", TextBox1.Text)

                'End write
                writer.WriteEndElement()
                writer.WriteEndDocument()
            End Using

        Else
            ' file already exist, next check if input data already exist            
            Dim myXmlDocument As XmlDocument = New XmlDocument()
            myXmlDocument.Load("D:\CampaignRewardsVoucher.xml")

            Dim myXMLNode As XmlNode = myXmlDocument.SelectSingleNode("CampaignRewardsVoucher")

            If myXMLNode IsNot Nothing And myXMLNode.ChildNodes(0).InnerText = DropDownList1.SelectedValue Then
                myXMLNode.ChildNodes(1).InnerText = TextBox1.Text

                myXmlDocument.Save("D:\CampaignRewardsVoucher.xml")
            Else

                'insert new node                
                'I need to insert Vouch002 here.

            End If

        End If

You can add a new child node at the desired position using XmlNode.InsertAfter

'...
Else
    Dim root As XmlNode = myXmlDocument.DocumentElement
    Dim vc As XmlElement = myXmlDocument.CreateElement("VoucherCode")
    vc.InnerText = "Vouch002"
    root.InsertAfter(vc, root.FirstChild)
End If
'...