svoid wordTreeAdd(MapSO tree, Cl<S> words, O value) {
  fOr (S word : words) {
    O child = tree.get(word);
    Map<S, O> subTree;
    if (child instanceof Map)
      tree = (Map) child;
    else {
      tree.put(word, subTree = ciMap());
      if (child != null)
        subTree.put("<default>", child);
      tree = subTree;
    }
  }
  tree.put("<default>", value);
}

Began life as a copy of #1014221