Help needed with .NET navigation controls

[rinishrk]

I have an website named Website1 with subfolders Admin and User within
it that contain web pages.I am generating a tree view for the website
that should allow me to have child nodes that redirect me to public
websites such as "www.yahoo.com" or "www.google.com". I created a
sitemap which looks as follows

<?xml version="1.0" encoding="utf-8" ?>
<siteMap xmlns="http://schemas.microsoft.com/AspNet/SiteMap-File-1.0" >
<siteMapNode url="/Home.aspx" title="Root" description="Root">
<siteMapNode url="/Admin/EditUser.aspx" title="Edit User"
description="Edit User" />
<siteMapNode url="/User/LoginFrom.aspx" title="LoginFrom"
description="LoginFrom" />
<siteMapNode url="www.google.com" title="Google"
description="Google" />
<siteMapNode url="www.yahoo.com" title="Yahoo"
description="Yahoo" />
</siteMapNode>
</siteMap>

But when the tree view get rendered,and i click on the child node
"Yahoo", it redirects me to the following link
"http://localhost/Website1/www.yahoo.com" instead of "www.yahoo.com" as
mentioned in the sitemap which is wrong.
Why does the treeview control append the virtual path of my website
i.e(http://localhost/Website1/)to each url i mention in the sitemap
when rendering the nodes????
How can i prevent it from doing so????