bootstrap-treeview为什么不显示收展按钮

代码如下：

 <script type="text/javascript">
        (function () {
            function getTree() {
                $.get("/get_department_tree/",
                  function(data){
                   {#data = JSON.parse(data);#}
                    if(data.result='ok'){
                       $('#tree').treeview({
                        data: data.data,
                        levels : 3,
                        showBorder: true,
                        showTags: true,
                        showCheckbox:1
                       });
                    }
                  });
            }
            getTree();

        })()
    </script>

数据格式是这样的：
{"data": [{"id": 1, "text": "总经办", "nodes": [{"id": 4, "text": "IT", "nodes": [{"id": 6, "text": "耗材"}], "tags": [1]}, {"id": 5, "text": "软件"}], "tags": [2]}, {"id": 2, "text": "项目部"}, {"id": 3, "text": "商务部", "nodes": [{"id": 7, "text": "采购"}], "tags": [1]}], "result": "ok"}

here : https://www.cnblogs.com/smxbo/p/12356591.html