cppreference.com > C++ Multisets > insert insert Syntax:
      #include <set>
      iterator insert( iterator pos, const TYPE& val );
      iterator insert( const TYPE& val );
      void insert( input_iterator start, input_iterator end );
The function insert() either: inserts val after the element at pos (where pos is really just a suggestion as to where val should go, since multisets and multimaps are ordered), and returns an iterator to that element. inserts val into the multiset, returning an iterator to the element inserted. inserts a range of elements from start to end.