code: def tree_attribute(identifier):
      
      if identifier[0].upper().isupper() is False and identifier[0] != '_':
          return True
      else:
          return identifier[0].isupper()
docs: Predicate that returns True for custom attributes added to AttrTrees
      that are not methods, properties or internal attributes.
  
      These custom attributes start with a capitalized character when
      applicable (not applicable to underscore or certain unicode characters)