SWI-Prolog unique random integer IDs in a list. That then belong to parent list

Using SWI-Prolog. How can I create a list of unique random integer IDs (with a list size between 2-5 IDs). These IDs will be added to a list called FG. A random number of FG lists will belong to a parent list called ND. ND will be made up of several FG lists. How can I create a loop that creates a FG, appends it to the ND list. Then it does it all over again?