A friend has a tart cherry tree that was with the home when they bought it. It's had gummosis on the main stem that's gotten progressively worse over the last several years. The tree is about 12' tall. The cherries are small and very tart until they turn a dark red then they are still mostly tart but have enough sweetness that they're great to eat fresh. The inside of the fruit is red and the flowers are white. They ripen in June.

They want to get the same type of tree placed far away so I need to know what type of sour cherry tree it is.

Any reasonably certain ID would be appreciated.