code: def filelist(self):
          
          if len(self._filelist) == 0:
              for item in self._data:
                  if isinstance(self._data[item], filetree):
                      self._filelist.extend(self._data[item].filelist())
                  else:
                      self._filelist.append(self._data[item])
          return self._filelist
docs: Return list of files in filetree.