\documentclass[varwidth=true, border=2pt]{standalone}
\usepackage[nomessages]{fp}
\usepackage{tikz}
\usetikzlibrary[topaths]
\begin{document}
\newcommand\n{5}
\begin{tikzpicture}
\node[vertex] (a) at (3,6) {};
\node[vertex] (b) at (2,4) {};
\node[vertex] (c) at (4,4) {};
\node[vertex] (d) at (1,2) {};
\node[vertex] (e) at (2,2) {};
\node[vertex] (f) at (3,2) {};
\node[vertex] (g) at (4,2) {};
\node[vertex] (h) at (0,0) {};
\node[vertex] (i) at (2,0) {};
\node[vertex] (j) at (3,0) {};
\node[vertex] (k) at (5,0) {};
\draw (a) -- (b);
\draw (a) -- (c);
\draw (b) -- (d);
\draw (b) -- (e);
\draw (b) -- (f);
\draw (d) -- (h);
\draw (d) -- (i);
\draw (c) -- (g);
\draw (g) -- (j);
\draw (g) -- (k);
\end{tikzpicture}
\end{document}