code: func (ot *orderedTree) Add(entries ...Entry) Entries {
  	if len(entries) == 0 {
  		return nil
  	}
  
  	overwrittens := make(Entries, len(entries))
  	for i, entry := range entries {
  		if entry == nil {
  			continue
  		}
  
  		overwritten := ot.add(entry)
  		if overwritten != nil {
  			overwrittens[i] = overwritten.entry
  		}
  	}
  
  	return overwrittens
  }
docs: // Add will add the provided entries to the tree.  This method
  // returns a list of entries that were overwritten in the order
  // in which entries were received.  If an entry doesn't overwrite
  // anything, a nil will be returned for that entry in the returned
  // slice.