string sql= "select * from plus_file order by id";
ds = db.getDataSet(sql);
ds.Relations.Add("TreeRelation", ds.Tables[0].Columns["Id"], ds.Tables[0].Columns["PId"]);
foreach (DataRow row in ds.Tables[0].Rows)
{
if (row.IsNull("PId"))
{
TreeNode node = new TreeNode();
node.Text = row["name"].ToString();
node.Expanded = true;
treeMenu.Nodes.Add(node);