code: def build(self, x):
          
          type = self._check_input(x)
  
          if type == 'st':
              x += next(self._terminalSymbolsGenerator())
              self._build(x)
          if type == 'gst':
              self._build_generalized(x)
docs: Builds the Suffix tree on the given input.
          If the input is of type List of Strings:
          Generalized Suffix Tree is built.
  
          :param x: String or List of Strings