easyUI 异步加载树

  $(function () {

        var selected = $('#depttree').tree('getSelected');
        $('#depttree').tree({
            checkbox: false,
            animate: true,
            url: '/Provider/HandlerCommon.ashx?method=getsessiontree',
            onClick: function (node) {

            }, onSelect: function (node) {
               // deptid = node.id;
            },
            onExpand: function (node) {
               // expandid = node.id;
            },
            onLoadSuccess: function (row, data) {

            }
        });
        });

 private string GetSessionTree(HttpContext context)
        {
            string parentid = context.Request["id"] == null ? "000" : context.Request["id"];
            StringBuilder sb = new StringBuilder();
            sb.Append("[");
            if (parentid.Length == 9)
            {
                DataCondition<EntitySequenceDepartment.Field> conditsequencedepartment = new DataCondition<EntitySequenceDepartment.Field>();
                conditsequencedepartment.Add("{0}='" + parentid + "'",EntitySequenceDepartment.Field.Sequence_Cur);
                IList<EntitySequenceDepartment> SequenceDepartmentList = DbSequenceDepartment .ListView(conditsequencedepartment);
                for (int i = 0; i < SequenceDepartmentList.Count; i++)
                {
                    sb.Append("{\"id\":\"" + SequenceDepartmentList[i].Sequence_Cur + "\",");
                    sb.Append("\"text\":\"" + SequenceDepartmentList[i].DepartmentName + "\",");
                    sb.Append("\"attributes\":\"" + SequenceDepartmentList[i].SeDepartment_Id + "\",");
                    sb.Append("\"state\":\"open\" },");
                }

            }
            else
            {
                DataCondition<EntitySequence.Field> conditionchild = new DataCondition<EntitySequence.Field>();
                conditionchild.Add("{0}='" + parentid + "'", EntitySequence.Field.Sequence_Parent);
                IList<EntitySequence> SequenceList = DbSequence.ListView(conditionchild);

                for (int i = 0; i < SequenceList.Count; i++)
                {
                    sb.Append("{\"id\":\"" + SequenceList[i].Sequence_Cur + "\",");
                    sb.Append("\"text\":\"" + SequenceList[i].Sequence_Name + "\",");
                    sb.Append("\"attributes\":\"" + SequenceList[i].Sequence_Id + "\",");

                    if (CheckSequence(SequenceList[i].Sequence_Cur))
                    {
                        sb.Append("\"state\":\"closed\" },");
                    }
                    else
                    {
                        if (CheckSequenceDepartment(SequenceList[i].Sequence_Cur))
                        {
                            sb.Append("\"state\":\"closed\" },");
                        }
                        else
                        {
                            sb.Append("\"state\":\"open\" },");
                        }
                    }

                }

            }
              sb.Remove(sb.Length - 1, 1);
                sb.Append("]");
            return sb.ToString();

        }