code: function RBT(compare, unique) {
    if (!(this instanceof RBT))
      return new RBT(compare, unique);
  
    assert(typeof compare === 'function');
  
    this.root = SENTINEL;
    this.compare = compare;
    this.unique = unique || false;
  }
docs: An iterative red black tree.
  @alias module:utils.RBT
  @constructor
  @param {Function} compare - Comparator.
  @param {Boolean?} unique