private void Initialize()
        {
            treeView.ItemsSource = StoreCollection.GetData();

            var ce = new CustomEngine();
            var cl = new CustomLexer();

            editor.SetCustomEngine(ce, cl);
            editor.DataSource = treeView.ItemsSource;
            editor.Expression = "[Name] + \": \" + [ProductsGroups].Where(x => x.Name == \"Notebooks\").Sum(x => x.Products.Sum(p => p.Count))";
        }