how can i create treeview depending on datagridview

hello.

i get data from two database db1, db2, into one datagridview, this dtatgridview has three columns[Id, Name, DirectorId], only the first row has no director, and each director has one or more child, so that i want to create treeview that have one main node, and each node can has one or more of childNode, for that, i declare :

public struct person
        {
            public string name;
            public string id;
            public string father;
        }

then convert datagridview into datatable:

public void ConverData()
        {
            DataTable dt = new DataTable();
            foreach (DataGridViewColumn col in DataGridView1.Columns)
            {
                dt.Columns.Add(col.HeaderText);
            }

            foreach (DataGridViewRow row in DataGridView1.Rows)
            {
                DataRow dRow = dt.NewRow();
                foreach (DataGridViewCell cell in row.Cells)
                {
                    dRow[cell.ColumnIndex] = cell.Value;
                }
                dt.Rows.Add(dRow);
            }
        }

after that i will get data from datagridview using LINQ, and convert these data to nodetree:

 public void setTree()
        {
           var per = (from n in dt.AsEnumerable()
                      select   new person()
                           {
                               name= n.Field<string>("Name"),
                               id = n.Field<string>("ID"),
                               father = n.Field<string>("Father")
                           }).ToList();

            var rootTreeNode = GetTree(per, "0").First();------------------------------------------------------------------(1)
            treeView1.Nodes.Add(rootTreeNode);

        }
        private TreeNode[] GetTree(List<person> per, string parent)
        {
            return per.Where(p => p.father == parent).Select(p =>
            {
                var node = new TreeNode(p.name);
                node.Tag = p.id;
                node.Nodes.AddRange(GetTree(per, p.id));
                return node;
            }).ToArray();
        }

when i test it, i get error at mark(1) above, that say: Additional information: Sequence contains no elements.

now, where is the error for solve it?

thank you very much