\begin{tikzpicture}[->,>=stealth,shorten >=1pt,auto,scale=0.6,transform shape]
	% x node set with absolute coordinates
	\node[state] (A) at (1.5,1.5) {$A$};
	\node[dstate] (X1) at (0,0) {$X_1$};
	\node[dstate] (X2) at (3,0) {$X_2$};
	\node[dstate] (Y1) at (0,-1.7) {$Y_1$};
	\node[dstate] (Y2) at (3,-1.7) {$Y_2$};
	\node[state] (C1) at (0,-3.4) {$C_1$};
	\node[state] (C2) at (3,-3.4) {$C_2$};
	% Directed edge
	\path (A) edge (X1);
	\path (A) edge (X2);
	\path (X1) edge (Y1);
	\path (X2) edge (Y2);
	\path (Y1) edge (C1);
	\path (Y2) edge (C2);

	% Bidirected edge
	%\path[bidirected] (A) edge[bend left=60] (C);
	%\node at ($(1)!.5!(2)$) {\ldots};
\end{tikzpicture}
