You need to wrap up child sitemapnodes in parent sitemapnode,
<siteMapNode url="~/Home.aspx" title="Home" description="Main site page">
<siteMapNode url="~/Movies.aspx" title="Movies" description="Movie store">
<siteMapNode url="~/Clothes.aspx" title="Clothes" description="Clothes Store" />
</siteMapNode>
</siteMapNode>
For further understanding, refer this article.