\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 [line] () to (a.north);}
    [$a$, name=a, tikz={\draw [line] () to (b1.north); \draw [fulldot=.5] () to (b2.north);}
        [$b$, name=b1, tikz={\draw [line] () to (c1.north); \draw [dot=.5] () to (c2.north);}
            [$c$, name=c1, tikz={\draw [line, bend right] () to (d1.north west); \draw [fulldot=.5, bend left] () to (d1.north east);}
                [$d$, name=d1, tikz={\draw [line] () to (249:6.37); \draw [fulldot=.5] () to (256:6.13);}]
            ]
            [$c$, name=c2, tikz={\draw [line] () to (258:4.7); \draw [fulldot=.5] () to (267:4.6);}]
        ]
        [$b$, name=b2, tikz={\draw [line] () to (c3.north); \draw [dot=.5] () to (c4.north);}
            [$c$, name=c3, tikz={\draw [line, bend right] () to (d2.north west); \draw [dot=.5, bend left] () to (d2.north east);}
                [$d$, name=d2, tikz={\draw [line] () to (272:5.9); \draw [fulldot=.5] () to (280:5.98);}]
            ]
            [$c$, name=c4, tikz={\draw [line] () to (288:4.83); \draw [fulldot=.5] () to (295:5.05);}]
        ]
    ]
]
\end{forest}
\end{center}