code: def render_json(tree, indent):
      
      return json.dumps([{'package': k.as_dict(),
                          'dependencies': [v.as_dict() for v in vs]}
                         for k, vs in tree.items()],
                        indent=indent)
docs: Converts the tree into a flat json representation.
  
      The json repr will be a list of hashes, each hash having 2 fields:
        - package
        - dependencies: list of dependencies
  
      :param dict tree: dependency tree
      :param int indent: no. of spaces to indent json
      :returns: json representation of the tree
      :rtype: str