\item \BDDToROBDD

\begin{center}
\begin{forest}
for tree={circle, draw, no edge,
            minimum size=2em,
            inner sep=0pt,
            s sep=2mm,
            l sep=2mm}
[$f$, rectangle, draw,  tikz={\draw [line] () to (a.north);}
    [$a$, name=a, tikz={\draw [line] () to (b1.north east); \draw [dot=.5] () to (b2.north west);}
        [$b$, name=b1, tikz={\draw [line] () to (c1.north); \draw [dot=.5] () to (c2.north);}
            [$c$, name=c1, tikz={\draw [line, bend right] () to (one.west); \draw [dot=.5, bend right] () to (zero.west);}]
            [$c$, l sep=15mm, name=c2, tikz={\draw [line, bend right] () to (one.north); \draw [dot=.5, bend left] () to (one.north east);}
                [$1$, rectangle, draw, name=one]
                [,phantom]
            ]
        ]
        [$b$, name=b2, tikz={\draw [line] () to (c3.north); \draw [dot=.5] () to (c4.north);}
            [$c$, l sep=15mm, name=c3, tikz={\draw [line, bend left] (.south) to (one.east); \draw [dot=.3, bend left] (.south east) to (one.south east);}
                [,phantom]
                [$0$, rectangle, draw, name=zero]
            ]
            [$c$, name=c4, tikz={\draw [line, bend left] (.south) to (zero.north); \draw [dot=.5, bend left] () to (zero.north east);}]
        ]
    ]
]
\end{forest}
\end{center}