public static ImmutableList<ChildNumber> append(List<ChildNumber> path, ChildNumber childNumber) {
        return ImmutableList.<ChildNumber>builder().addAll(path).add(childNumber).build();
    }
public static ImmutableList < ChildNumber > append ( List < ChildNumber > path , ChildNumber childNumber ) { return ImmutableList . < ChildNumber > builder ( ) . addAll ( path ) . add ( childNumber ) . build ( ) ; }
Append a derivation level to an existing path