Pressure Cooked Wheat Berry And Chickpea Stew

• 9 chunks (peeled)
• 4 parsnips
• 3 stalks celery
• 2 bay leaves
• 1 onion coarsely (chopped)
• 3/8 loosely packed mustrooms (dried)
• 1,400 ml vegetable stock
• 190 gr wheat berries picked over (whole)
• 150 gr chickpeas picked over (dried)
• 28 gr butter