What you see here is two different plants expressing themselves. The roots and trunk of this Cherry tree is a generic “Cherry tree” – used for its vigorous roots and straight trunk. To the side of the tree is a piece of Weeping Cherry tree that was grafted onto the bottom. This is how a Weeping Cherry is created. Most Weeping Cherries do not grow with their own roots – they are carefully spliced to the vigorous root stock. Think about the younger Weeping Cherry trees that you see around town – they often look like umbrellas with a bone straight trunk and weeping poof on the top. Two plants stuck together.
In this photo, you can see that the root stock, the generic Cherry tree, has started to grow branches upward while the grafted Weeping Cherry clings to the side. The root stock Cherry is more energetic and will overtake the weaker Weeping Cherry scion. This problem should have been stopped several years ago by cutting off the generic Cherry when it started to grow. Now you would have to remove it in phases so as not to kill the overall tree.
You can sometimes see this happen with weeping Japanese Maples too. Moral of the story – Watch your plants!