How to insert new item to channel in XML file

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VB

ASP.NET

I want to insert new element inside <channel> tag using vb code
my xml file looks like :

<?xml version="1.0" encoding="utf-8"?>
<rss version="2.0" xmlns:media="http://search.yahoo.com/mrss/">
<channel>

</channel>
</rss>

this is my code :

Dim root = New XElement("item")
    Dim title = New XElement("title", New XCData(TextBox3.Text))
    Dim link = New XElement("link", TextBox6.Text)
    Dim pubDate = New XElement("pubDate", DateTime.Now.ToString("yyy/MM/dd HH:mm"))
    Dim description = New XElement("description", New XCData(TextBox5.Text))
    Dim thumbnail = New XElement("media.thumbnail",
                                  New XAttribute("url", "http://karary-001-site1.htempurl.com/files/" + attac1 + "?itok=YdFLolAU"),
                                  New XAttribute("height", 266),
                                  New XAttribute("width", 127))
    root.Add(title, link, pubDate, description, thumbnail)
    document.Root.Add(root)
    document.Save(FilePath)

my code add new items after channel and rss tag end !!

What I have tried:

add my element's to the root element's first element using :
document.Root.Elements.First().Add(root)