Two runners occupying the same base

[Bart]

Here is the situation: John is batting, Mike is on 1B and Carl is on 2B. John hits a blooper to the outfield it, was a no catch by the outfielder, but the play was close enough so that the runners didn’t know if the outfielder would catch the ball. Once Mike (on 1B) sees that the catch wasn’t made he runs for 2B. Carl (on 2B) doesn’t move. The outfielder gets to the ball and throws it to 2B in time to beat Mike, and force an out in a normal situation. The ump calls Mike safe. But now we have Mike and Carl both standing on 2B. The second baseman tags Carl and Mike but the ump says he doesn’t see the tag, so Carl runs for 3B, the throw is dropped by the third baseman. Eventual result of the play is everyone is safe.

My question is not that the ump didn’t see the tag or the force, but can you have 2 runners occupying the same base at the same time?