<<< native
[ ESub
    (EIdentifier "A")
    (ESub (EIdentifier "B") (ESub (EIdentifier "C") (EIdentifier "D")))
, ESymbol Rel "="
, ESub
    (EIdentifier "A")
    (ESub
       (EIdentifier "B")
       (ESub
          (EIdentifier "C")
          (ESub (EIdentifier "D") (EPhantom (EIdentifier "E")))))
]
>>> omml
<?xml version='1.0' ?>
<m:oMathPara>
  <m:oMathParaPr>
    <m:jc m:val="center" />
  </m:oMathParaPr>
  <m:oMath>
    <m:sSub>
      <m:e>
        <m:r>
          <m:t>A</m:t>
        </m:r>
      </m:e>
      <m:sub>
        <m:sSub>
          <m:e>
            <m:r>
              <m:t>B</m:t>
            </m:r>
          </m:e>
          <m:sub>
            <m:sSub>
              <m:e>
                <m:r>
                  <m:t>C</m:t>
                </m:r>
              </m:e>
              <m:sub>
                <m:r>
                  <m:t>D</m:t>
                </m:r>
              </m:sub>
            </m:sSub>
          </m:sub>
        </m:sSub>
      </m:sub>
    </m:sSub>
    <m:r>
      <m:rPr>
        <m:sty m:val="p" />
      </m:rPr>
      <m:t>=</m:t>
    </m:r>
    <m:sSub>
      <m:e>
        <m:r>
          <m:t>A</m:t>
        </m:r>
      </m:e>
      <m:sub>
        <m:sSub>
          <m:e>
            <m:r>
              <m:t>B</m:t>
            </m:r>
          </m:e>
          <m:sub>
            <m:sSub>
              <m:e>
                <m:r>
                  <m:t>C</m:t>
                </m:r>
              </m:e>
              <m:sub>
                <m:sSub>
                  <m:e>
                    <m:r>
                      <m:t>D</m:t>
                    </m:r>
                  </m:e>
                  <m:sub>
                    <m:phant>
                      <m:phantPr>
                        <m:show m:val="0" />
                      </m:phantPr>
                      <m:e>
                        <m:r>
                          <m:t>E</m:t>
                        </m:r>
                      </m:e>
                    </m:phant>
                  </m:sub>
                </m:sSub>
              </m:sub>
            </m:sSub>
          </m:sub>
        </m:sSub>
      </m:sub>
    </m:sSub>
  </m:oMath>
</m:oMathPara>