code: func (sl *SkipList) Insert(comparators ...common.Comparator) common.Comparators {
  	overwritten := make(common.Comparators, 0, len(comparators))
  	for _, cmp := range comparators {
  		overwritten = append(overwritten, sl.insert(cmp))
  	}
  
  	return overwritten
  }
docs: // Insert will insert the provided comparators into the list.  Returned
  // is a list of comparators that were overwritten.  This is expected to
  // be an O(log n) operation.