treegrid报错 Uncaught TypeError: Cannot read property 'length' of undefined

[
    {
        "id":"1",
        "name":"系统设置",
        "level":1,
        "children":[
            {
                "id":"1",
                "name":"菜单管理",
                "type":"1",
                "iswhite":"0",
                "level":2,
                "children":[
                    {
                        "id":"2",
                        "name":"菜单管理",
                        "parentid":"1",
                        "iswhite":"0",
                        "level":3,
                        "children":[
                            {
                                "id":"3",
                                "name":"菜单列表",
                                "parentid":"2",
                                "iswhite":"0",
                                "level":4
                            },
                            {
                                "id":"4",
                                "name":"菜单添加",
                                "parentid":"2",
                                "iswhite":"0",
                                "level":4
                            },
                            {
                                "id":"5",
                                "name":"菜单删除",
                                "parentid":"2",
                                "iswhite":"0",
                                "level":4
                            },
                            {
                                "id":"6",
                                "name":"菜单白名单",
                                "parentid":"2",
                                "iswhite":"0",
                                "level":4
                            }
                        ]
                    }
                ]
            }
        ]
    },
    {
        "id":"6",
        "name":"测试大1",
        "level":1,
        "children":[
            {
                "id":"18",
                "name":"测试中11",
                "type":"6",
                "iswhite":"0",
                "level":2,
                "children":[

                ]
            }
        ]
    },
    {
        "id":"2",
        "name":"看板",
        "level":1,
        "children":[
            {
                "id":"14",
                "name":"测试1",
                "type":"2",
                "iswhite":"0",
                "level":2,
                "children":[
                    {
                        "id":"15",
                        "name":"看看",
                        "parentid":"14",
                        "iswhite":"0",
                        "level":3,
                        "children":[

                        ]
                    }
                ]
            }
        ]
    }
]