static Map<S, O> parseDoubleArrowTreeCI(S text) {
  L<S> lines = withoutEmpties(rtrimAll(lines(text)));
  if (empty(lines)) null;

  new L<Map<S, O>> nodes;
  new L<Int> indents; // indent of children
  
  nodes.add(ciMap());
  indents.add(countIndent(first(lines)));
  
  for (S s : lines) {
    int indent = countIndent(s);
    
    while (indent < last(indents)) {
      removeLast(nodes);
      removeLast(indents);
    }
    
    L<S> x = splitAtDoubleArrow(s);
    if (l(x) == 2) // leaf
      last(nodes).put(first(x), second(x));
    else {
      Map<S, O> newTree = ciMap();
      last(nodes).put(s, newTree);
      nodes.add(newTree);
      indents.add(indent+1);
    }
  }
  
  ret tree;
}