\begin{frame}
  \frametitle{Parse Trees}
  
  What is the formula corresponding to the following parse tree?
  \bigskip
  \begin{center}
  \begin{tikzpicture}[default]
    \begin{scope}[tree,nodes={node_yellow,minimum size=6mm}]
    %!begin{tree}{magic:006780749442385126}
    % $\to$:e($\wedge$:l($\neg$:ll($p$:lll),$q$:lr),$\wedge$:r($p$:rl,$\vee$:rr($q$:rrl,$\neg$:rrr($r$:rrrr))))
\node (e) {$\to$}
    child { node (l) {$\wedge$}
      child { node (ll) {$\neg$}
        child { node (lll) {$p$}
      }
    }
      child { node (lr) {$q$}
    }
  }
    child { node (r) {$\wedge$}
      child { node (rl) {$p$}
    }
      child { node (rr) {$\vee$}
        child { node (rrl) {$q$}
      }
        child { node (rrr) {$\neg$}
          child { node (rrrr) {$r$}
        }
      }
    }
  };
\begin{pgfonlayer}{background}
\end{pgfonlayer}

    %!end{tree}{magic:006780749442385126}
    \end{scope}
    
    \begin{scope}[dgreen]
    \mpause[1]{ 
      \node [lhead=lll] {$p$};
    }
    \mpause{ 
      \node [rhead=lr] {$q$};
      \node [lhead=rl] {$p$};
      \node [lhead=rrl] {$q$};
      \node [rhead=rrrr] {$r$};
    }
    \mpause{ 
      \node [lhead=ll] {$\neg p$};
    }
    \mpause{ 
      \node [lhead=l] {$\neg p \wedge q$};
    }
    \mpause{ 
      \node [rhead=rrr] {$\neg r$};
    }
    \mpause{ 
      \node [rhead=rr] {$q \vee \neg r$};
    }
    \mpause{ 
      \node [rhead=r] {$p \wedge (q \vee \neg r)$};
    }
    \mpause{ 
      \node [ahead=e] (l) {$(\neg p \wedge q) \to (p \wedge (q \vee \neg r))$};
    }
    \mpause{ 
      \node [ahead=l] (l) {$\neg p \wedge q \to p \wedge (q \vee \neg r) = $};
    }
    \end{scope}
  \end{tikzpicture}
  \end{center}
\end{frame}