private void DeleteSelectedStudent(object sender, RoutedEventArgs e)
 {
     if (selectedStudent is object)
     {
         currentList.DeleteFirst(selectedStudent);
         Refresh();
     }
 }
        private void DeleteCurrentGroup(object sender, RoutedEventArgs e)
        {
            MessageBoxResult messageBoxResult = MessageBox.Show("Are you sure?", "Delete Confirmation", MessageBoxButton.YesNo);

            if (messageBoxResult == MessageBoxResult.Yes && !(selectedFaculty is null))
            {
                selectedFaculty.DeleteFirst(selectedGroup);
                Refresh();
                OnPropertyChanged("CanDeleteGroup");
            }
        }