箱线图添加圆圈/星号

Question

关于如何在图中添加圆圈或星号（*），有什么建议吗？

\pgfplotsset{width=7cm,compat=1.16}\usepgfplotslibrary{statistics}
\begin{tikzpicture}
\begin{axis}[
boxplot/draw direction=y,
x axis line style={opacity=0},
axis x line*=bottom,
axis y line=left,
enlarge y limits,
ymajorgrids,
xtick={1,2,3},
xticklabels={Seltenheit, normierter Preis, Group C},
]
\addplot+ [
boxplot prepared={
lower whisker=2, lower quartile=3,
median=5.5,
upper quartile=10, upper whisker=10,
},
] table [row sep=\\,y index=0] {6\\ };
\addplot+ [
boxplot prepared={
lower whisker=3, lower quartile=4,
median=4.5,
upper quartile=5, upper whisker=5,
},
] table [row sep=\\,y index=0] {5.17\\ };
coordinates {};
 coordinates {(0,35) (0,55)};
  \drawcircle (0,8)
\end{axis}
\end{tikzpicture}