(((x12 & x20) & x05) | x02) | ((x12 & x13)) | (x13 | x20)

import re
string = '(((x12 & x20) & x05) | x02) | ((x12 & x13)) | (x13 | x20)'
result = re.findall('(([^(].*?))', string)
# --> ['x12 & x20', 'x12 & x13', 'x13 | x20']
print('({})'.format(result[0]))