\item \BDDToROBDD

\begin{center}
\begin{forest}
for tree={circle, draw, no edge,
            minimum size=2em,
            inner sep=0pt,
            s sep=5mm,
            l sep=5mm}
[$f$, rectangle, draw,  tikz={\draw [fulldot=.5] () to (a.north);}
    [$a$, name=a, tikz={\draw [line] () to (b1.north); \draw [dot=.5] () to (b2.north);}
        [$b$, name=b1, tikz={\draw [line] () to (d1.north); \draw [dot=.5] () to (260:3.3);}
            [$d$, name=d1, tikz={\draw [line] () to (c1.north); \draw [fulldot=.5] () to (255:4.6);}
                [$c$, name=c1, tikz={\draw [line] () to (243:6.5); \draw [dot=.5] () to (253:6.05);}]
                [,phantom]
            ]
            [,phantom]
        ]
        [$b$, name=b2, tikz={\draw [line] () to (d2.north); \draw [dot=.5] () to (300:3.7);}
            [$d$, name=d2, tikz={\draw [line] () to (c2.north); \draw [fulldot=.5] () to (286:4.7);}
                [$c$, name=c2, tikz={\draw [line] () to (265:5.8); \draw [dot=.5] () to (275:5.8);}]
                [,phantom]
            ]
            [,phantom]
        ]
    ]
]
\end{forest}
\end{center}