\begin{tikzpicture}[every tree node/.style={draw,circle},sibling distance=.25cm]
\Tree
 [.$\lor$ 
    [.$P$ $x$ $y$ ]
    [.$\exists y$
        [.$\forall x$
            [.$\land$ 
                [.$Q$ $x$ $y$ ]
                [.$R$ $y$ $z$ ]
            ]
        ]
    ]
 ]
\end{tikzpicture} 
\newline \\
Free variables: $x, y, z$ \\
Bound variables: $x, y$