linq to xml check for duplicates, any equals

I have xml file

<Nodes>
   <Node> one </Node>
   <Node> two </Node>
   <Node> three </Node>
</Nodes>

inside method I'm receving list of nodes to append into file, so I want to check is there duplicates

public static void AppendToXmlFile(List<string> passedNodes)
{
    bool duplicates = passedNodes.Any(x=>x.Equals(doc.Element("Nodes")
                                 .Descendants("Node")
                                 .Select(a=>a.Value))); 
...
}

this query always returns false.