Count the number of smaller numbers from my right (array)

count.smaller.js

//given an array arr, you have to return the amount of numbers that are smaller than arr[i] to the right.
// BSTree, complexity O(n squared)

var smaller = function (nums) {
  var res = [], count = 0, i = nums.length - 2,thisCount = 0;
  if (nums == null || nums.length == 0) return res;
  var root = NewTreeNode(nums[nums.length - 1]);
  res.push(0);
  for (; i >= 0; i--) {
    res.push(insertNodeAndCount(root, nums[i]));
  }

  //mutates&returns
  return res.reverse();
}

var insertNodeAndCount = function (root, val) {
  thisCount = 0;
  while (true) {
    if (val <= root.val) {
      root.count++;
      if (root.sm == null) {
        root.sm = NewTreeNode(val); break;
      } else {
        root = root.sm;
      }
    } else {
      thisCount += root.count;
      if (root.big == null) {
        root.big = NewTreeNode(val); break;
      } else {
        root = root.big;
      }
    }
  }
  return thisCount;
}

var NewTreeNode = function(val) {
 return {
    sm: undefined,
    big: undefined,
    val,
    count: 1
  }
}

console.log(smaller([5, 4, 3, 2, 1]), [4, 3, 2, 1, 0]);
console.log(smaller([1, 2, 3]), [0, 0, 0]);
console.log(smaller([1, 2, 0]), [1, 1, 0]);
console.log(smaller([1, 2, 1]), [0, 1, 0]);
console.log(smaller([1, 1, -1, 0, 0]), [3, 3, 0, 0, 0]);
console.log(smaller([5, 4, 7, 9, 2, 4, 4, 5, 6]), [4, 1, 5, 5, 0, 0, 0, 0, 0]);