[Tex/LaTex] Line break with equations in game tree labels produced with TikZ

equationsline-breakingtikz-pgftrees

I use this manual for help with the drawing of game trees using TikZ (http://www.sfu.ca/~haiyunc/notes/Game_Trees_with_TikZ.pdf).

However, I have a challenge I cannot seem to overcome. Some of my end-nodes require line breaks in the labels. In the concrete example below, in the end node on the left in the second branch (after "Not Resist"), I would like the equation after the two vertical lines (||) to be placed below the first equation. In other words split the line between the X and the U_S.

I have tried by specifying "align=centre" and using \\ but it did not work. Similarly, I tried specifying an equation environment within the label, but it did not work either.

Any help would be most appreciated.

An MWE:

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{tikz}
\begin{document}

\tikzset{
    solid node/.style={circle,draw,inner sep=1.5,fill=black},
    hollow node/.style={circle,draw,inner sep=1.5}
}

\begin{tikzpicture}[scale=1.5,font=\footnotesize]
    \tikzstyle{level 1}=[level distance=15mm, sibling distance=20mm]
    \tikzstyle{level 2}=[level distance=15mm, sibling distance=20mm]
          \node(0)[solid node,label=above:{\textbf{Sender}}]{}
              child{node(1)[hollow node, label=below:{$U_S(SQ)$}]{}
              edge from parent node[left,xshift=-3,yshift=5]{\textit{Not Threaten}}
              }
              child{node(2)[solid node, label=above right:{\textbf{Target}}]{}
                  child{node[hollow node, label=below:{$U_S(TS)=X$ \\ $||U_T(TS)=Y$}]{} edge from parent node[left,xshift=-3,yshift=0]{\textit{Not Resist}}}
                  child{node[hollow node, label=below:{$TF$}]{} edge from parent node[right,xshift=3,yshift=0]{\textit{Resist}}}
                  edge from parent node[right,xshift=3,yshift=5]{\textit{Threaten}}
                  };
  \end{tikzpicture}

\end{document}

A game tree model

Best Answer

You may use \makecell:

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{tikz}
\usepackage{makecell}
\begin{document}

\tikzset{
    solid node/.style={circle,draw,inner sep=1.5,fill=black},
    hollow node/.style={circle,draw,inner sep=1.5}
}

\begin{tikzpicture}[scale=1.5,font=\footnotesize]
    \tikzstyle{level 1}=[level distance=15mm, sibling distance=20mm]
    \tikzstyle{level 2}=[level distance=15mm, sibling distance=20mm]
          \node(0)[solid node,label=above:{\textbf{Sender}}]{}
              child{node(1)[hollow node, label=below:{$U_S(SQ)$}]{}
              edge from parent node[left,xshift=-3,yshift=5]{\textit{Not Threaten}}
              }
              child{node(2)[solid node, label=above right:{\textbf{Target}}]{}
                  child{node[hollow node, label=below:{\makecell{$U_S(TS)=X$ \\ $||U_T(TS)=Y$}}]{} edge from parent node[left,xshift=-3,yshift=0]{\textit{Not Resist}}}
                  child{node[hollow node, label=below:{$TF$}]{} edge from parent node[right,xshift=3,yshift=0]{\textit{Resist}}}
                  edge from parent node[right,xshift=3,yshift=5]{\textit{Threaten}}
                  };
  \end{tikzpicture}

\end{document}

enter image description here

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