\begin{tikzpicture}
	\foreach \pos [count=\xi] in { (1, 3), (2.5,4), (0, 2), (3, 2), (-1, 5), (1, 6) }
		\node[vertex] (v-\xi) at \pos {$\xi$};
	
	\foreach \v/\u in {1/4,1/5,1/2,1/3,3/4,3/5,5/2,2/4,1/6,5/6,2/6}
		\draw (v-\v) -- (v-\u);
\end{tikzpicture}