Splits the input file into the 'merge file' (which contains
        the EDUs) and the 'parsetree file'.

def split_input(self, input_filepath):
        """Splits the input file into the 'merge file' (which contains
        the EDUs) and the 'parsetree file'."""
        with open(input_filepath, 'r') as input_file:
            input_file_str = input_file.read()
            merge_file_str, parsetree_str = input_file_str.split('ParentedTree', 1)
            return merge_file_str, 'ParentedTree' + parsetree_str