binarySearchTree.js

function BinarySearchTree(val) {
  this.value = val;
  this.left = null;
  this.right = null;
}

BinarySearchTree.prototype.insert = function(value) {
  let subtree = value < this.value ? 'left' : 'right';
  if (this[subtree]) {
    this[subtree].insert(value);
  } else {
    this[subtree] = new BinarySearchTree(value);
  }
};