\documentclass{standalone}

\usepackage{tikz}

\begin{document}

\begin{tikzpicture}
  \node[draw,circle,label= left:{$x_1=-1$}] (0) at (0, 0) {0};
  \node[draw,circle,label=above:{$x_1=0$}] (1) at (1, 1) {1};
  \node[draw,circle,label=right:{$x_1=1$}] (2) at (2, 0) {2};

  \path[draw] (0) -- (1);
  \path[draw] (1) -- (2);
\end{tikzpicture}

\end{document}
