\documentclass[12pt]{standalone}

\usepackage{tikz}
\usepackage{ctex}

\tikzset{tree/.style={every node/.style={circle, draw}}}

\begin{document}
\begin{tikzpicture}

\scoped[tree] \node at (-2,0) {$y$}
    child[missing]
    child {node {$x$}};

\scoped[tree] \node at (2,0) {$x$}
    child {node {$y$}}
    child[missing];

\node at (0,-2.5) {2};

\draw[->] (-0.5,-0.75) -- ++(1,0);

\end{tikzpicture}
\end{document}