code: def _create_target_tree(self, target):
          
          source = self
          with source.walker as walker:
  
              @walker.folder_visitor
              def visit_folder(folder):
                  """
                  Create the mirror directory
                  """
                  if folder != source:
                      Folder(folder.get_mirror(target, source)).make()
docs: There is a bug in dir_util that makes `copy_tree` crash if a folder in
          the tree has been deleted before and readded now. To workaround the
          bug, we first walk the tree and create directories that are needed.