How to execute parallel test cases in Unittest framework in python?

I've tried the following method in test suite file:

import unittest
import xmlrunner
from ui_tests.test_prelogin import PreLoginTests

login_tests = unittest.TestLoader().loadTestsFromTestCase(PreLoginTests)

test_suite = unittest.TestSuite([login_tests])
unittest.main(testRunner=xmlrunner.XMLTestRunner(output='test-reports')).run(test_suite)