drawing trees with forest

Question

i want to draw a tree with thicker branches like the one in the picture, what could i put instead of ''thick'' ?

\documentclass[border=3.141592]{standalone}
\usepackage{forest}
\begin{document} 
\begin{forest}
for tree={grow=0}
[$A$,for tree={edge={red ,thick}}
[$V $,edge label={node[pos=0.7,left ,font= \small]{$x$}}
[$G$[.][.]][$H$[.][.]]]
[$EF$[$J$[.][.]][$K$[.][.]]]]
\end{forest}
\end{document}

Answer 1

Well, before will be closed ... some off topic suggestion:

• it is not clear (to me) if you like to change line width for only one edge, branch of edges, or for all edges
• in example are shown all possibilities
• added are styles for edge labels
• added are nodes stale math content

\documentclass[border=3.141592]{standalone}
%\documentclass{article}
\usepackage{forest}
\usetikzlibrary{arrows.meta}
\begin{document}
    \begin{forest}
for tree={
% nodes
    inner sep=2pt,
    math content,
% tree
    grow=0,
    edge={semithick},%     edge = arr,
        },
%% edge labels
/tikz/ELS/.style = {% Edge Label Style
                    node font=\scriptsize, text=cyan,
                    inner sep=0pt, 
                    pos=0.5, anchor=#1 east},
EL/.style = {if n=1{edge label={node[ELS=north]{$#1$}}}
                   {edge label={node[ELS=south]{$#1$}}}}
%%%% diagram body
[A,
    [V, for tree={edge={red ,ultra thick}}  % lower branch  will be red and ultra thick
      , EL=x
        [G, EL=u    [.][.]]
        [H, EL=v    [.][.]]
    ]
    [EF, EL=y, edge={blue,thick}            % only for one edge
        [J[.][.]]
        [K[.][.]]
    ]
]
\end{forest}
\end{document}