How Do I Save My Wounded Cherry Tree?!

Calling all experienced gardeners!! Help!

I just found an open wound on my Lapin Cherry tree I got from Miller Nurseries! The tree is only about 4′ tall now, has 5 branches and lots of buds that look like they will branch out in spring.

The wound is a yucky looking hole that’s rather soft when you feel around it. It’s in the top 1/3 of the trunk.

In the photos, you can see the hole toward the bottom of the picture.

So. Do I cut the trunk down to just above that branch below the hole? Is there another way to save the tree? I can’t just leave it the way it is… can I?