参考一下  
public void InitTree()
        {

            try
            {
                OleDbDataAdapter sqlda = new OleDbDataAdapter("select *from 部门 ",MyConn);
                DataSet ds = new DataSet();
                sqlda.Fill(ds, "部门");
                DataTable dt = ds.Tables["部门"];

                foreach (DataRow row in dt.Rows)
                {
                    TreeNode nox = new TreeNode();
                    id = row["编号"].ToString();
                    OleDbCommand myComm = new OleDbCommand("select count(*) as dd from 员工基本资料 where 部门编号='" + id + "'", MyConn);
                    int qty=Show(myComm.ExecuteScalar());
                    nox.Text = row["名称"].ToString()+"("+qty.ToString()+"人)";
                    nox.ExpandAll();

                    this.treeView1.Nodes.Add(nox);
                    FillTree(nox);
                }
            }
            catch (Exception Err)
            {
                MessageBox.Show(Err.Message);
            }
        }


        //FillTree(TreeNode   nod)建立子节点   
        public void FillTree(TreeNode nod)
        {
            try
            {
                OleDbDataAdapter sql = new OleDbDataAdapter("select   *   from   分公司   where   did='" + id + "'", MyConn);
                DataSet ds = new DataSet();
                sql.Fill(ds, "分公司");
                DataTable dt = ds.Tables["分公司"];


                foreach (DataRow row in dt.Rows)
                {
                    TreeNode temp = new TreeNode();

                    did = row["pno"].ToString();
                    temp.Text = string.Format("{0,   -20}", row["cname"].ToString().Trim());
                    temp.Tag = row["pno"].ToString(); ;
                    temp.ExpandAll();
                    nod.Nodes.Add(temp);
                    

                    

                }
                
            

            }
            catch (Exception Err)
            {
                MessageBox.Show(Err.Message);
            }

        }