code: def place(self, part: str, val: Union['ApiNode', 'ApiEndpoint']):
          
          if part.startswith(':'):
              if self.param and self.param != part:
                  err = """Cannot place param '{}' as '{self.param_name}' exist on node already!"""
                  raise ParamAlreadyExist(err.format(part, self=self))
              self.param = val
              self.param_name = part
              return val
          self.paths[part] = val
          return val
docs: place a leaf node