\begin{tikzpicture}
  \tikzset{every node/.style={shape=circle,draw,inner sep=2pt}}

\node (a) at (-0.5, 0) {$a$};
\node (e) at (-1.0, 1) {$e$};
\node (b) at (0.0, 1) {$b$};
\node (d) at (-1.0, 2) {$d$};
\node (c) at (0.0, 2) {$c$};

\draw (a) -- (e);
\draw (b) -- (c);
\draw (e) -- (d);
\draw (a) -- (b);
\draw (e) -- (c);

\end{tikzpicture}