# How do I add an arrow and text to Halo in Tikz?

I was wondering how I can add an arrow coming from the circled region as shown in Tikz and also adding some text to the end of the arrow . Here is what I have so far

\usetikzlibrary{backgrounds}
\begin{document}

\begin{tikzpicture}[halo/.style={line join=round,
double,line cap=round,double distance=#1,shorten >=-#1/2,shorten <=-#1/2},
halo/.default=7mm]
\node[circle,draw,fill=gray](s){s}
child{node[circle,draw,fill=white]{}
child{node[circle,draw,fill=gray]{}}
}
child{node[circle,draw,fill=white]{}
child{node[circle,draw,fill=gray]{}}
}
child{node[circle,draw,fill=white](R1){}
child{node[circle,draw,fill=gray](R2){}}
};
\begin{scope}[on background layer]
\draw[halo] (s) -- (R1.center) -- (R2);
\end{scope}
\path (R2.south) ++ (0,-3.5mm); % shorten does not get taken into account by the bounding box
\end{tikzpicture}
\end{document}


Like this?

\documentclass[tikz,border=3mm]{standalone}
\usetikzlibrary{backgrounds,calc}
\begin{document}

\begin{tikzpicture}[halo/.style={line join=round,
double,line cap=round,double distance=#1,shorten >=-#1/2,shorten <=-#1/2},
halo/.default=7mm]
\node[circle,draw,fill=gray](s){s}
child{node[circle,draw,fill=white]{}
child{node[circle,draw,fill=gray]{}}
}
child{node[circle,draw,fill=white]{}
child{node[circle,draw,fill=gray]{}}
}
child{node[circle,draw,fill=white](R1){}
child{node[circle,draw,fill=gray](R2){}}
};
\begin{scope}[on background layer]
\draw[halo] (s) -- (R1.center) coordinate[pos=0.8] (tip) -- (R2);
\end{scope}
\path (R2.south) ++ (0,-3.5mm); % shorten does not get taken into account by the bounding box
\draw[stealth-] ($(tip)!3.5mm!-90:(s)$) to[bend right=20]
($(tip)!1.2cm!-90:(s)$) node[above]{text};
\end{tikzpicture}
\end{document}