\documentclass[tikz,border=10pt]{standalone}
                        \IfFileExists{newpxtext.sty}{\usepackage{newpxtext,newpxmath}}{}
                        \linespread{1.10}
                        \usetikzlibrary{shapes}
                        \usetikzlibrary{arrows.meta}
                        \usepackage{graphicx}

                        \begin{document}

                        % TikZ code with built-in styling for game trees
% TikZ libraries required for game trees
\usetikzlibrary{shapes}
\usetikzlibrary{arrows.meta}

% Style settings for game tree formatting
\tikzset{
    every node/.append style={font=\sffamily\itshape},
    every text node part/.append style={align=center},
    node distance=1.5mm,
    thick
}

% Built-in macro definitions for game tree drawing
\newdimen\ndiam
\ndiam1.5mm
\newdimen\sqwidth
\sqwidth1.6mm
\newdimen\spx
\spx.7mm
\newdimen\spy
\spy.5mm
\newdimen\paydown
\paydown2.5ex
\newdimen\treethickn
\treethickn1.0pt
\definecolor{chancecolor}{RGB}{117,145,56}
\definecolor{p1rgb}{RGB}{0,127,255}
\definecolor{p2rgb}{RGB}{221,121,224}

% Game tree content from /home/docs/checkouts/readthedocs.org/user_builds/gambitproject/checkouts/latest/catalog/books/shohamleytonbrown2008/fig5_12__original_layout.ef
\begin{tikzpicture}[scale=0.8
  , StealthFill/.tip={Stealth[line width=.7pt,inset=0pt,length=13pt,angle'=30]}]
% \draw [help lines, color=green] (-5,0) grid (5,-6);
\draw [line width=\treethickn,draw=none,color=p1rgb,fill=p1rgb,fill opacity=0.2] (0.208,-0.312) arc(-56.3:123.7:0.375)
  -- (-3.208,-1.688) arc(123.7:303.7:0.375) -- cycle;
%% % Extensive-form game transcribed from the uploaded image
%% player 1 name 1
\def\playerone{1}
%% player 2 name 2
\def\playertwo{2}
%% % Player 1's two decision nodes are in the same information set.
%% level 0 node 1
\draw [line width=\treethickn] (0,-0)
   ;
%% level 2 node 1 xshift -3 from 0,1 move L
\draw [line width=\treethickn,color=p1rgb] (-3,-2)
   -- (0,-0);
\draw (-1.5,-1) node[left,xshift=-0.5mm,color=p1rgb] {L\strut};
%% level 2 node 2 xshift 3 from 0,1 move R player 2
\draw [line width=\treethickn,color=p1rgb] (3,-2)
   -- (0,-0);
\draw (1.5,-1) node[right,xshift=0.5mm,color=p1rgb] {R\strut};
%% level 4 node 1 xshift -1 from 2,1 move L payoffs 1 0
\draw [line width=\treethickn,color=p1rgb] (-4,-4)
   node[below,yshift=0.1\paydown,color=p1rgb] {$\mathsf{1}\strut$}
   node[below,yshift=-0.9\paydown,color=p2rgb] {$\mathsf{0}\strut$}
   -- (-3,-2);
\draw (-3.5,-3) node[left,xshift=-0.5mm,color=p1rgb] {L\strut};
%% level 4 node 2 xshift 1 from 2,1 move R payoffs 100 100
\draw [line width=\treethickn,color=p1rgb] (-2,-4)
   node[below,yshift=0.1\paydown,color=p1rgb] {$\mathsf{100}\strut$}
   node[below,yshift=-0.9\paydown,color=p2rgb] {$\mathsf{100}\strut$}
   -- (-3,-2);
\draw (-2.5,-3) node[right,xshift=0.5mm,color=p1rgb] {R\strut};
%% level 4 node 3 xshift -1 from 2,2 move U payoffs 5 1
\draw [line width=\treethickn,color=p2rgb] (2,-4)
   node[below,yshift=0.1\paydown,color=p1rgb] {$\mathsf{5}\strut$}
   node[below,yshift=-0.9\paydown,color=p2rgb] {$\mathsf{1}\strut$}
   -- (3,-2);
\draw (2.5,-3) node[left,xshift=-0.5mm,color=p2rgb] {U\strut};
%% level 4 node 4 xshift 1 from 2,2 move D payoffs 2 2
\draw [line width=\treethickn,color=p2rgb] (4,-4)
   node[below,yshift=0.1\paydown,color=p1rgb] {$\mathsf{2}\strut$}
   node[below,yshift=-0.9\paydown,color=p2rgb] {$\mathsf{2}\strut$}
   -- (3,-2);
\draw (3.5,-3) node[right,xshift=0.5mm,color=p2rgb] {D\strut};
%% iset 0,1 2,1 player 1
\node[inner sep=0pt,minimum size=\ndiam,draw=p1rgb,fill=p1rgb,shape=circle] at (0,-0) {};
\node[inner sep=0pt,minimum size=\ndiam,draw=p1rgb,fill=p1rgb,shape=circle] at (-3,-2) {};
\node[inner sep=0pt,minimum size=\ndiam,draw=p2rgb,fill=p2rgb,shape=circle] at (3,-2) {};

% Player color legend
\begin{scope}[scale=1,shift={(-5.5,-0.0)}]
\node[inner sep=0pt,minimum size=\ndiam,draw=p1rgb,fill=p1rgb,shape=circle] at (0,0) {};
\node[anchor=west] at (0.3,0) {1};
\node[inner sep=0pt,minimum size=\ndiam,draw=p2rgb,fill=p2rgb,shape=circle] at (0,-0.625) {};
\node[anchor=west] at (0.3,-0.625) {2};
\end{scope}

\end{tikzpicture}

                        \end{document}