code: function toTree(arr, low, high) {
  	if (low >= high) {
  		return undefined;
  	}
  	var mid = Math.floor((high + low) / 2);
  	return {
  		el: arr[mid],
  		right: toTree(arr, mid + 1, high),
  		left: toTree(arr, low, mid)
  	};
  }
docs: Build a balanced binary tree from an ordered array.