58. get DOM tree height

Height of a tree is the maximum depth from root node. Empty root node have a height of 0.

If given DOM tree, can you create a function to get the height of it?

For the DOM tree below, we have a height of 4.

<div>
  <div>
    <p>
      <button>Hello</button>
    </p>
  </div>
  <p>
    <span>World!</span>
  </p>
</div>

Can you solve this both recursively and iteratively?