Node.prototype.push = function(n) {
  if (this.value === null) {
    this.value = n
    return
  }

  if (n < this.value) {
    if (this.left === null) {
      this.left = new Node(n)
    } else {
      this.left.push(n)
    }
  } else {
    if (this.right === null) {
      this.right = new Node(n)
    } else {
      this.right.push(n)
    }
  }
}