\begin{center}
\begin{forest}
for tree={circle, draw, no edge,
            minimum size=2em,
            inner sep=0pt,
            s sep=6mm,
            l sep=6mm}
[$f$, rectangle, draw,  tikz={\draw [line] () to (s.north);}
    [$s$, name=s, tikz={\draw [line] () to (-0.6, -2.2); \draw [fulldot=.5] () to (r.north);}
        [,phantom]
        [$r$, name=r, tikz={\draw [line] () to (p.north); \draw[dot=.5] () to (1.3,-3.5);}
            [$p$, name=p, tikz={\draw [line] () to (-0.6, -4.8); \draw[fulldot=.5] () to (0.6, -4.8);}]
            [,phantom]
        ]
    ]
]
\end{forest}
\end{center}