[Tex/LaTex] Draw an arrow between nodes in forest

Question

I want to create an arrow between two nodes like the red one in below example.

I've seen the following in documentation, but tbh I don't understand how to use it and I need to use it in more than one tree.

Answer 1

It works precisely as described in the documentation...

\documentclass[tikz,border=3.14mm]{standalone}
\usepackage[edges]{forest}
\begin{document}
\tikzset{state/.style={draw,circle}}
\forestset{d/.style={dotted,edge=dotted},
r/.style={red,edge=red}}
\begin{forest}
for tree={state,edge={-},grow=south,l sep=6mm,s sep=10mm},
[22,d
 [13,d
  [30,red,edge=dotted
   [15,r]
   [85,r]{\draw[<->,red] () to[bend right=45] node[midway,above
   right,font=\small]{zam} (!u.east);}
  ]
  [71
   [17]
   [20]
  ]
 ]
 [11,d
  [33,edge=dotted
   [32]
  ]
  [55,d]
 ]
]
\end{forest}
\end{document}