class Less::Node::Expression

def _to_sass_tree2(first, rest)
  return first if rest.empty?
  if rest[0].is_a?(Operator)
    op = LESS_TO_SASS_OPERATORS[rest[0]]
    if op == :times || op == :div
      second, rest = _sass_split(rest[1..-1])
      return _to_sass_tree2(Sass::Script::Operation.new(first, second, op), rest)
    else
      return Sass::Script::Operation.new(first, _to_sass_tree(rest[1..-1]), op)
    end
  end
  Sass::Script::Operation.new(first, _to_sass_tree(rest), :concat)
end