VS 2019 always says ,,Method must have a return type" and i don't know whats wrong

So i work on a Program which needs to get an File-Explorer, on which I am currently working on. However, my problem is that I always get the error "Method must have a return type" in line 174 (Line 7 counted from bottom to top) and I've tried everything but I can't fix the error.

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace WpfApp1
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        private DriveInfo drive;

        public MainWindow()
        {
            InitializeComponent();
        }


      --------------------- unnecessary code cutted ----------------------------


        void item_Expanded(object sender, RoutedEventArgs e)
        {
            var item = (TreeViewItem)sender;
            if (this.HasDummy(item))
            {
                this.Cursor = Cursors.Wait;
                this.RemoveDummy(item);
                this.ExploreDirectories(item);
                this.ExploreFiles(item);
                this.Cursor = Cursors.Arrow;
            }
        }

        public MainWindow()
        {
            InitializeComponent();
            this.LoadDirectories();
        }
    }
}