Here my Code:

 <ig:WebHierarchicalDataGrid ID="WebHierarchicalDataGrid1" runat="server" AutoGenerateColumns="false"
            AutoGenerateBands="false"  InitialExpandDepth="0" InitialDataBindDepth="0" Height="450"
            Width="100%" DataKeyFields="id" StyleSetName="Office2007Blue"            
            OnPreRender="WebHierarchicalDataGrid1_PreRender" EnableViewState="False"
            OnRowIslandsPopulating="WebHierarchicalDataGrid1_RowIslandsPopulating"
            OnRowIslandDataBound="WebHierarchicalDataGrid1_RowIslandDataBound"
            >
                
            <ExpandCollapseAnimation SlideOpenDirection="Auto" SlideOpenDuration="300" SlideCloseDirection="Auto"
                SlideCloseDuration="300" />

              
                <Columns>
                    <ig:TemplateDataField Key="chkChon">
                        <ItemTemplate>
                            <asp:CheckBox ID="chkChon"
                            runat="server" Enabled="true" Checked="false" />
                        </ItemTemplate>                    
                    </ig:TemplateDataField>
                    
                     <ig:BoundDataField Hidden="False" DataFieldName="id" Key="id">
                        <Header Text="id" />

                    </ig:BoundDataField>             
                    <ig:BoundDataField DataFieldName="code" Key="code">
                        <Header Text="Mã" />
                    </ig:BoundDataField>
                    <ig:BoundDataField DataFieldName="name" Key="name">
                        <Header Text="Tên đơn vị" />
                    </ig:BoundDataField>
                
                                
               
                        
                </Columns>
                <Bands>                    
                    <ig:Band
                    Key="id" DataKeyFields="id" ShowHeader="false"
                        AutoGenerateColumns="False">
                        <Columns>
                            <ig:TemplateDataField Width="10%" Key="chkChon">
                                <ItemTemplate>
                                    <asp:CheckBox ID="chkChon"  runat="server"
                                     Enabled="true" Checked="false" />
                                </ItemTemplate>                    
                            </ig:TemplateDataField>
                             <ig:BoundDataField Hidden="True" Width="20%" DataFieldName="id" Key="id" ><Header Text="Mã"></Header>
                            </ig:BoundDataField>
                            <ig:BoundDataField Width="20%" DataFieldName="username" Key="username" ><Header Text="Mã"></Header>
                            </ig:BoundDataField>

                            <ig:BoundDataField Width="35%" DataFieldName="name" Key="name" >
                                <Header Text="Tên cán bộ"></Header>
                            </ig:BoundDataField>
                            
                            <ig:BoundDataField DataFieldName="dept_name" Key="dept_name" >
                                <Header Text="Phòng ban"></Header>
                            </ig:BoundDataField>
                            
                             
                        </Columns>
                    </ig:Band>
                </Bands>  
                
            </ig:WebHierarchicalDataGrid>

<asp:Button ID="cmdSave" OnClick="cmdSave_OnClick" runat="server" Text="Save" />

 protected void WebHierarchicalDataGrid1_RowIslandsPopulating(object sender, ContainerRowCancelEventArgs e)
        {
            
            e.Cancel = true;

            var childGrid = new ContainerGrid();

            // Get the data key

            string key = e.Row.DataKey[0].ToString();

            var sql =
                @"SELECT u.[id],
                   u.[username],
                   u.[name],
                   u.[branch_id],
                   b.name AS dept_name
            FROM   admin.[user] u
                   INNER JOIN list.branch b
                        ON  b.id = u.unit_id
                   INNER JOIN admin.user_group ug
                        ON  ug.[user_id] = u.id
            WHERE  ug.group_id =" +
                Request.QueryString["id"] + " and u.branch_id =" + key;


            if (rdo1.Checked)
            {
                sql =
                @"SELECT u.[id],
                   u.[username],
                   u.[name],
                   u.[branch_id],
                   b.name AS dept_name
            FROM   admin.[user] u
                   INNER JOIN list.branch b
                        ON  b.id = u.unit_id                   
            WHERE  u.branch_id =" + key;

            }
            DataSet dsTemp = DbUtil.DbUtil.get_dataset(sql);


            if (dsTemp != null && dsTemp.Tables[0].Rows.Count > 0)
            {

                e.Row.RowIslands.Add(childGrid);
                
                childGrid.DataSource = dsTemp;

                childGrid.Band = WebHierarchicalDataGrid1.Bands[0];

            }

            if (WebHierarchicalDataGrid1.GridView.Rows[e.Row.Index].RowIslands != null
               && WebHierarchicalDataGrid1.GridView.Rows[e.Row.Index].RowIslands.Count > 0)
            {
                var childGrid2 = WebHierarchicalDataGrid1.GridView.Rows[e.Row.Index].RowIslands[0];
                foreach (GridRecord record in childGrid2.Rows)
                {
                    var c = record.Items[0].FindControl("chkChon") as CheckBox;

                    var sql1 = @"Select count(1) as total from admin.user_group ug where ug.group_id="
                              + Request.QueryString["Id"] + " and ug.user_id= " + record.Items[1].Value;
                    var a = DbUtil.DbUtil.get_datarow(sql1);
                   
                    if (a != null && a["total"].Equals(1) && c != null)
                        c.Checked = true;

                }
            }
           
          


        }

protected void WebHierarchicalDataGrid1_RowIslandDataBound(object sender, RowIslandEventArgs e)
        {
            if (WebHierarchicalDataGrid1.GridView.Rows[0].RowIslands.Count > 0)
            {
                var childGrid2 = WebHierarchicalDataGrid1.GridView.Rows[0].RowIslands[0];
                
                                        foreach (GridRecord record in childGrid2.Rows)
                                        {
                                            var c = record.Items[0].FindControl("chkChon") as CheckBox;
                                                           
                                            if (c!= null && c.Checked)
                                                userListId += record.Items[1].Value + ";";                            
                                        }
            }

        }

        protected void cmdSave_OnClick(object sender, EventArgs e)
        {
            var session = NHibernateSessionManager.Instance.Session;

            try
            {
                session.BeginTransaction();

              
                string userListId = "";

                foreach (GridRecord row in WebHierarchicalDataGrid1.Rows)
                {
                    var b = row.Items[0].FindControl("chkChon") as CheckBox;
                    
                    // Get row island using data member
                    if (WebHierarchicalDataGrid1.GridView.Rows[row.Index].RowIslands != null &&
                        WebHierarchicalDataGrid1.GridView.Rows[row.Index].RowIslands.Count > 0)
                    {
                        var childGrid2 = WebHierarchicalDataGrid1.GridView.Rows[row.Index].RowIslands[0];

                        foreach (GridRecord record in childGrid2.Rows)
                        {
                            var c = record.Items[0].FindControl("chkChon") as CheckBox;

                            if (record.Items[2].Value.Equals("thuynt.bic"))
                            {
                                string x = "1";
                            }
                            if (c!= null && c.Checked)
                                userListId += record.Items[1].Value + ";";                            
                        }
                    }


                }

                if(userListId.Length > 0)
                {
                    userListId = userListId.Substring(0, userListId.Length - 1);

                    var sql = "exec acc.sp_phan_quyen_nguoi_dung_theo_nhom " + Request.QueryString["Id"] + ",'" + userListId + "'";

                    DbUtil.DbUtil.get_datatable(sql);

                }

                session.CommitTransaction();

                lblMessage.Text = "Cập nhật thành công!";

                
            }catch(Exception ex)
            {
                lblMessage.Text = ex.Message;

                session.RollbackTransaction();
            }

        }

but WebHierarchicalDataGrid1.GridView.Rows[row.Index].RowIslands  is no data