Add two tablespoons of oil to the Instant Pot, and heat on saute mode. Toss the stew meat with the salt and pepper. Add the beef to the pot and cook, turning frequently, until browned on all sides (you may need to do this in two batches).
Remove the beef from the pot and add the remaining tablespoon of oil and the onion, leek, and garlic to the pot. Cook, scraping the browned bits from the bottom of the pot, until the onion is soft and translucent.
In a medium bowl, whisk together the tomato paste, beef stock, Worcestershire, and thyme. Add the bay leaves, celery, carrots, potatoes, rutabaga, turnip, and celery root to the pot. Add the browned beef to the pot. Pour the broth mixture over the top and stir gently to combine.
Place the lid on the Instant Pot, turn the knob to seal, and set it to cook on manual mode at high pressure for 35 minutes.
When the cook time is finished, let the pressure naturally release for 10-15 minutes, then quick release the remaining pressure. In a small bowl, whisk together the corn starch and water until the corn starch is dissolved. Pour the corn starch mixture into the pot and stir until the stew is slightly thickened.
Taste and add additional salt and pepper if needed. Serve hot with fresh parsley on top.