documentclass[11pt]{article}

newcommand{ccg}[2]{
begin{tabular}[t]{c}
%begin{tabular}[t]{@{}c@{}}
#1\hline
#2
end{tabular}
}

begin{document}
%setlengthtabcolsep{-3pt}
ccg{ccg{Mary}{$NP$}
     ccg{ccg{loves}{$(Sbackslash NP)/NP$}
          ccg{John}{$NP$}
         }{$Sbackslash NP$}
    }{$S$}

end{document}