如何在树视图中填充多个子级别？

Question

我的 TreeView 中存在一个问题，我只能填充一个级别的子级，例如

Parent Level 0

---->Child Level 1

   ---->Child Level 2  //here i'm not able to get this level

我的问题是我无法在 TreeView 中获得 Child Level 2 这是我的aspx.cs代码

 protected void Page_Load(object sender, EventArgs e)
    {
        if (!this.IsPostBack)
        {
            DataTable dt0 = this.GetData("select ClientId,C_Name from clientdetails");
            this.PopulateTreeView(dt0, 0, null);


            TreeView1.Attributes.Add("onclick", "return OnTreeClick(event)");
            TreeView1.CollapseAll();
         }

    }



    private void PopulateTreeView(DataTable dtParent, int parentId, TreeNode treeNode)//this is for parent Level 0 node
    {
        foreach (DataRow row in dtParent.Rows)
        {
            TreeNode child = new TreeNode
            {
                Text = row["C_Name"].ToString(),
                Value = row["ClientId"].ToString()
            };
            if (parentId == 0)
            {
                //TreeNode node = new TreeNode();
                //node.Text = "par";
                TreeView1.Nodes.Add(child);
                DataTable dtChild1 = this.GetData("SELECT location_id, Location_name FROM client_locations WHERE client_id = " + child.Value);
                PopulateTreeView1(dtChild1, int.Parse(child.Value), child);
            }
            else
            {
                treeNode.ChildNodes.Add(child);
            }
        }
    }

    private void PopulateTreeView1(DataTable dtParent, int parentId, TreeNode treeNode)//this is for Child  Level 1 node
    {
        foreach (DataRow row in dtParent.Rows)
        {
            TreeNode child = new TreeNode
            {
                Text = row["Location_name"].ToString(),
                Value = row["location_id"].ToString()
            };
            if (parentId == 0)
            {
                TreeView1.Nodes.Add(child);
                DataTable dtChild = this.GetData("SELECT contactperson_id, concat(fname,' ',lname)as name FROM contactpersons WHERE Location_id = " + child.Value);
                PopulateTreeView2(dtChild, int.Parse(child.Value), child);

            }
            else
            {
                treeNode.ChildNodes.Add(child);
            }
        }
    }

    private void PopulateTreeView2(DataTable dtParent, int parentId2, TreeNode treeNode)//this is for Child  Level 2 node here its not working 
    {
        foreach (DataRow row in dtParent.Rows)
        {
            TreeNode child = new TreeNode
            {
                Text = row["contactperson_id"].ToString(),
                Value = row["name"].ToString()
            };
            if (parentId2 == 0)
            {
                TreeView1.Nodes.Add(child);
                DataTable dtChild = this.GetData("SELECT contactperson_id, concat(fname,' ',lname)as name FROM contactpersons WHERE Location_id = " + child.Value);
                //PopulateTreeView2(dtChild, int.Parse(child.Value), child);

            }
            else
            {
                treeNode.ChildNodes.Add(child);
            }
        }
    }

我应该修改什么才能让我的孩子达到2级水平？