How to search TreeNodeAdv based on its tag value in WinForms TreeViewAdv?

List<TreeNodeAdv> nodes;
// To search all nodes
nodes = treeViewAdv1.SearchTree().Where(n => n.Tag == "Search node").ToList();

public static class SOExtension
{
    public static IEnumerable<TreeNodeAdv> SearchTree(this TreeViewAdv treeView)
    {
        return SearchTree(treeView.Nodes);
    }

    public static IEnumerable<TreeNodeAdv> SearchTree(this TreeNodeAdvCollection coll)
    {
        return coll.Cast<TreeNodeAdv>().Concat(coll.Cast<TreeNodeAdv>().SelectMany(x => SearchTree(x.Nodes)));
    }
}

Private nodes As List(Of TreeNodeAdv)
'To search all nodes
nodes = treeViewAdv1.FlattenTree().Where(Function(n) n.Tag = "Search node").ToList()

Public Module SOExtension
    <System.Runtime.CompilerServices.Extension()> _
    Public Function SearchTree(ByVal treeView As TreeViewAdv) As IEnumerable(Of TreeNodeAdv)
        Return SearchTree(treeView.Nodes)
    End Function

    <System.Runtime.CompilerServices.Extension()> _
    Public Function SearchTree(ByVal coll As TreeNodeAdvCollection) As IEnumerable(Of TreeNodeAdv)
        Return coll.Cast(Of TreeNodeAdv)().Concat(coll.Cast(Of TreeNodeAdv)().SelectMany(Function(x) SearchTree(x.Nodes)))
    End Function
End Module