\begin{tikzpicture}[->,>=stealth,shorten >=1pt,auto,scale=\rthinning,transform shape]
	% x node set with absolute coordinates
	\node[state] (A) at (0,0) {$A$};
	\node[dstate] (B) at (-1.5,-1.5) {$B$};
	\node[dstate] (C) at (1.5,-1.5) {$C$};
	\node[state] (D) at (-1.5,-3.5) {$D$};
	\node[state] (E) at (1.5,-3.5) {$E$};
	\node[state] (F) at (0,-5) {$F$};
	% Directed edge
	\path (A) edge (B);
	\path (A) edge (C);
	\path (B) edge (D);
	\path (B) edge (E);
	\path (C) edge (D);
	\path (C) edge (E);
	\path (D) edge (F);
	\path (E) edge (F);
	% Bidirected edge
	%\path[bidirected] (A) edge[bend left=60] (C);
\end{tikzpicture}
