\documentclass[a4paper,12pt]{report} 
\usepackage{tikz}

\tikzstyle{vertex}=[circle, draw, inner sep=0pt, minimum size=8pt] 
\newcommand{\vertex}{\node[vertex]}

\tikzstyle{vertexs}=[draw,minimum width=.2cm,minimum height=.2cm]
\newcommand{\vertexs}{\node[vertexs]}
\begin{document}
\[
\begin{tikzpicture} 
\vertex [fill](a1) at (0,0) [label=left:$0$]{};
\vertex [fill](b1) at (0,-3.5) [label=left:$1$]{};
\vertexs [fill](a2) at (3.5,0) [label=right:$0$]{};
\vertexs [fill](b2) at (3.5,-3.5) [label=right:$1$]{};


\path
(a1) edge (a2)
(a1) edge (b2)
(b1) edge (a2)
(b1) edge (b2);
\end{tikzpicture}
\]
\end{document}