code: def list_to_tree(cls, files):
          
  
          def attach(branch, trunk):
              """Insert a branch of directories on its trunk."""
              parts = branch.split('/', 1)
              if len(parts) == 1:  # branch is a file
                  trunk[FILE_MARKER].append(parts[0])
              else:
                  node, others = parts
                  if node not in trunk:
                      trunk[node] = defaultdict(dict, ((FILE_MARKER, []), ))
                  attach(others, trunk[node])
  
          tree = defaultdict(dict, ((FILE_MARKER, []), ))
          for line in files:
              attach(line, tree)
          return tree
docs: Converts a list of filenames into a directory tree structure.