text: from typing import Any, List, Dict
  from lib.json_helper import JSONHelper
  
  
  class ExternalTrees:
      @staticmethod
      def parse(config: Dict[str, Any]) -> str:
          external_tree_string: str = ""
          external_tree: Dict[str, Any]
          JSONHelper.parse_attr(config, "external_trees", list, fail=True)
          external_trees: List[str] = config["external_trees"]
  
          for external_tree in external_trees:
              external_tree_string += (
                  JSONHelper.parse_attr(external_tree, "name")[1] + ":"
              )
          return external_tree_string[:-1]
  