Add in the onions and carrots and saute for 3 minutes. Then add in celery and garlic and saute for 1 minute longer.
Carefully add in the chicken broth and tomatoes, then add in the oregano, basil, and bay leaf.
Place the lid on the pot and make sure that the knob on the top is on "sealing". Turn off the "saute" and press the "manual" (or pressure cook) button on your Instant Pot. Set the timer for 5 minutes (it will take about 10 minutes to come to pressure, so be sure to factor that in).
Once it's finished cooking, let it do a 5-10 minute natural release (i.e. don't touch the knob and just let it sit there), then move the knob on top to "venting" to release whatever pressure is left.
Carefully remove the lid and turn the Instant Pot back to back to the saute function.
Slowly pour in the half and half, whisking the entire time you pour and mixing until it's fully incorporated. Let it cook for a few minutes on the saute setting.
Whisk in the milk and the Parmesan cheese, then add salt and pepper to taste.
Ladle into bowls and top with fresh basil and Parmesan cheese.
Recipe by Tone and Tighten at https://tone-and-tighten.com/instant-pot-creamy-tomato-basil-soup.html