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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def tree_attribute(identifier):
 """ 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) """

    if identifier[0].upper().isupper() is False and identifier[0] != '_':
        return True
    else:
        return identifier[0].isupper()