\documentclass[12pt]{standalone}

\usepackage{tikz}
\usepackage{ctex}

\begin{document}
\begin{tikzpicture}

\scoped[every node/.style={circle,draw}]
\node {1}
    child {node {2}
        child {node {5}}
        child {node {6}}}
    child {node {3}}
    child {node {4}
        child {node {7}
            child {node {8}}}};

\end{tikzpicture}
\end{document}
