TreeView生成树形结构

public void InitData()
        {
            using (var db = new HJSDR_BJXH_20170303_TESTEntities())
            {
                pyFiles = new PyFiles();
                TreeNode rootNode = null;
                TreeNode typeNode = null;
                foreach (var item in db.ED_KPI_INFO)
                {
                    if (!tv_singal.Nodes.ContainsKey(item.SD_CODE))
                    {
                        rootNode = new TreeNode(item.SD_CODE);
                        rootNode.Name = item.SD_CODE;
                        tv_singal.Nodes.Add(rootNode);
                    }
                    if (!rootNode.Nodes.ContainsKey(item.KPI_TYPE_CODE))
                    {
                        typeNode = new TreeNode(item.KPI_TYPE_CODE);
                        typeNode.Name = item.KPI_TYPE_CODE;
                        rootNode.Nodes.Add(typeNode);
                    }
                    if (typeNode != null)
                    {
                        typeNode.Nodes.Add(item.KPI_NAME,item.KPI_NAME);
                    }
                }
               
            }