C# Select TreeNode by Tag from DataGridViewRow index

Question

BACKGROUND

I have a DataGridView table that populates a TreeView with TreeNodes. The TreeNode.Tag property value is determined by the table RowIndex. When I select a Cell in the table the TreeView node with the selected tablerowindex as tag should also be selected and it's parent expanded.

But how do I get the nodes tag value and compare it to the RowIndex? I use this extention method to get all TreeNode objects from the TreeView as follows

var select = from node in treeView.Descendants()
             where (node.Tag as string) == e.RowIndex.ToString()
             select node as TreeNode;

But var select return an empty WhereSelectListIterator? Where did I go wrong?

UPDATE 1

The TreeNode where TreeNode.Tag is the IndexRow is at TreeNode.Level 3 and the Descendants() method only return root level nodes and root level child nodes, and that is why my WhereSelectListIterator is empty.

The question is now How do I get the Descendants() method to include TreeNodes at TreeNode.Level 3?

UPDATE 2

Instead of using the Descendants() method I use this extention method to get a list of all TreeNodes in TreeView and it included all nodes no matter what level.

But now I cannot compare the node.Tag to the e.RowIndex?

The method this far:

private void headerGridView_CellClick(object sender, DataGridViewCellEventArgs e)
    {
        List<TreeNode> oNodeList = treeView.GetAllNodes();

        var select = from node in oNodeList
                     where (node.Tag as string) == e.RowIndex.ToString()
                     select node as TreeNode;
        foreach (TreeNode node in select)
        {
            // This never happens because the select is empty
        }
    }

I tested the oNodeList like this so I know(!) there is nodes with tags in the list.

StringBuilder sb = new StringBuilder();
foreach (TreeNode node in oNodeList)
{
    if (node.Tag != null) sb.AppendLine(node.Name);
}
MessageBox.Show(sb.ToString());

SOLUTION

I found a solution to my problem. There is really no need to use Linq to select nodes and add to a WhereSelectListIterator. The solution was much simpler than that.

private void headerGridView_CellClick(object sender, DataGridViewCellEventArgs e)
{
    List<TreeNode> oNodeList = treeView.GetAllNodes();
    foreach (TreeNode node in oNodeList)
    {
        if (node.Tag == null) continue;
        if ((int)node.Tag == e.RowIndex)
        {
            treeView.SelectedNode = node;
            if (!treeView.SelectedNode.Parent.IsExpanded) treeView.SelectedNode.Parent.Expand();
        }
    }
}

CONCLUTION

Don't over complicate things.