It's not a Bultaco, it's a much more humble motorcycle used to transport the masses after the war.
This bike was produced for many years and in many different configurations.
One more interesting thing about it is that it was conceived first as a different bike!
Here is another picture for you, showing an earlier bike.
You got it right of course
The DKW 125 was an extremely good design for the tiome and the allies took over the drawings and rights to produce it after the war.
The Bantam was produced in UK by BSA for many years and in large numbers.
It's a very popular bike in UK and many are restored.