WPF 递归数据绑定到ComboBox上

我的数据库设计是这样的。

代码是这么写的。

public TypeAdd()
        {
            InitializeComponent();

            ObservableCollection<XModel.STORE_TYPE> list = XDAL.STORE_TYPE_DAL.GetData();
            this.fl_state.DisplayMemberPath = "Stype_name";
            this.fl_state.SelectedValuePath = "Stype_code";
            ObservableCollection<XModel.STORE_TYPE> listx = new ObservableCollection<STORE_TYPE>(list.Where(item => item.Parent_stype_code == ""));
            foreach (var item in listx)
            {
                treelist.Add(item);
                Get(item.Stype_code, list);
            }

            foreach (var item in treelist)
            {
                int limitLower = (Convert.ToInt32(item.Stype_level.Length) / 8);
                for (int i = 0; i < limitLower; i++)
                {
                    if (limitLower == 1)
                    {
                        item.Stype_name += "=>";
                    }
                    else
                    {
                        item.Stype_name = item.Stype_name.Insert(0, "     ");
                    }
                }
            }
            treelist.Insert(0, new XModel.STORE_TYPE()
            {
                Stype_name = "顶级分类",
                Stype_code = ""
            });
            this.fl_state.ItemsSource = treelist;
            this.fl_state.SelectedIndex = 0;

        }
        public void Get(string parendId,ObservableCollection<XModel.STORE_TYPE> cache)
        {
           ObservableCollection<XModel.STORE_TYPE> list = new ObservableCollection<STORE_TYPE>(cache.Where(u=>u.Parent_stype_code==parendId));
            if (list.Count==0)
            {
                return;
            }
            foreach (var item in list)
            {
                treelist.Add(item);
                Get(item.Stype_code, cache);
            }
        }
        ObservableCollection<XModel.STORE_TYPE> treelist = new ObservableCollection<STORE_TYPE>();

效果是这样的。