<<< native
[ ESuper
    (ENumber "2")
    (ESuper (ENumber "3") (ESuper (ENumber "4") (ENumber "5")))
, ESymbol Rel "="
, ESuper
    (ENumber "2")
    (ESuper
       (ENumber "3")
       (ESuper
          (ENumber "4") (ESuper (ENumber "5") (EPhantom (ENumber "6")))))
]
>>> tex
2^{3^{4^{5}}} = 2^{3^{4^{5^{\phantom{6}}}}}