\documentclass[preview]{standalone}
\usepackage{qtree}
\begin{document}

\Tree[.Expression
        [.Add
            [.Expression
                [.Add
                    [.Expression Num(3) ]
                    [.Plus(+) ]
                    [.Expression Num(2) ]]]
            [.Plus(+) ]
            [.Expression Num(1) ]]]

\end{document}
