Mulberries can produce as early as one year after planting, depending on the variety, some can take longer. One of mine made fruit just a few months after I planted it, but the fruit didn't develop fully, as the plant was still adjusting to being transplanted.
As was already mentioned by others above, berries and the Prunus genus (plums, cherries, peaches, and others) have fruited earliest for me. Most plums and peaches bloom really early here in zone 7b, so in zone 6a you may want to look for varieties of plums and peaches that bloom later to avoid early Spring frosts. My Prunus fruit trees that were planted in rich, well draining soil, have exploded with lots of growth and some have grown more that 4 ft. their first year in the ground.
I've heard that training the tree branches of fruit trees that normally take longer to fruit, to droop down and also limiting their nitrogen can help them produce fruit earlier.
I prefer to plant standard size trees in the ground if possible. They seem to grow fast and be very low maintenance that way. If you moved, you could take cuttings with you to start new trees, and maybe potential buyers would be looking for a home with some good fruit trees and bushes!
Hope you get some tasty fruit soon!
