usepackage{mathtools}


makeatletter
newcommand{superimpose}[2]{%
  {ooalign{$#1@firstoftwo#2$crhfil$#1@secondoftwo#2$hfilcr}}}
makeatother
newcommand{MyTry}{mathpalettesuperimpose{{sum}{vert}}}

begin{document}
 $MyTry$
end{document}