树

\begin{document}
	\begin{tikzpicture}[scale=2, ultra thick,
	every node/.style={draw=black, circle, very thick, font =\huge, minimum size=3em},
	level 1/.style={sibling distance=4em/1, level distance=4em},%横向距离与纵向距离
	level 2/.style={sibling distance=4em/2, level distance=4em},
	level 3/.style={sibling distance=4em/1, level distance=4em},
	]
	\node(1) {S1}
		child {node (2) {S2}
			child {node (4) {S4}}
			child {node (5) {S5}}
		}
        child {node[draw=red, fill=red!50] (3) {S3}
			child {node[rectangle, xshift=2.5cm] (6) {S6}}
		};
	\end{tikzpicture}
\end{document}