<<< native
[ ESuper
    (EIdentifier "v")
    (ESuper
       (EIdentifier "w")
       (ESuper
          (EIdentifier "x") (ESuper (EIdentifier "y") (EIdentifier "z"))))
]
>>> mml
<?xml version='1.0' ?>
<math display="block" xmlns="http://www.w3.org/1998/Math/MathML">
  <msup>
    <mi>v</mi>
    <msup>
      <mi>w</mi>
      <msup>
        <mi>x</mi>
        <msup>
          <mi>y</mi>
          <mi>z</mi>
        </msup>
      </msup>
    </msup>
  </msup>
</math>