% TeX root = ../main.tex
\begin{tikzpicture}[program,initial above,font=\scriptsize]
    \node[state,initial]    (l0)                       {$\ell_0$};
    \node[state] (l1) [below=2cm of l0] {$\ell_1$};
    \node[state] (l2) [right=5cm of l1] {$\ell_2$};
    \node[state] (l3) [below=2cm of l1] {$\ell_3$};
    \path[->]   
        (l0) edge node[swap]{ $t_0$ } (l1)
        (l1) edge node[swap]{ $t_1: \tau = x > 0$ } (l2)
        (l1) edge node[swap]{ $t_4: \tau = x \leq 0$ } (l3)
        (l2) edge[color=rot-75,bend right=60] node { $t_{2a}:
        \begin{aligned}&p=0.5\\&\tau=y < z\end{aligned}$ } (l1)
        (l2) edge[color=rot-75,bend right=80] node[swap] { $t_{2b}:
        \begin{aligned}&p=0.5\\&\tau=y < z\\&\eta(y)=y+1\end{aligned}$ } (l1)
        (l2) edge[color=rwth-75,bend left=60] node[swap] {
        $t_{3a}:\begin{aligned}&p=0.5 \\&\tau=y \geq z\end{aligned}$ } (l1)
        (l2) edge[color=rwth-75,bend left=80] node {
        $t_{3b}:\begin{aligned}&p=0.5 \\&\tau=y \geq z\\&\eta(x) = x-1\end{aligned}$ } (l1)
                    ;
\end{tikzpicture}

% TeX root = ../main.tex
\begin{tikzpicture}[program,initial above,font=\scriptsize]
    \node[state,initial]    (l0)                       {$\ell_0$};
    \node[state] (l10) [below=2cm of l0] {$\ell_{1,0}$};
    \node[state] (l30) [below=2cm of l10] {$\ell_{3,0}$};
    \node[state] (l21) [right=3cm of l10] {$\ell_{2,1}$}; % rename to l20
    \node[state] (l11) at ($(2,-3)+(l21)$) {$\ell_{1,1}$};
    \node[state] (l13) at ($(-2,-3)+(l21)$) {$\ell_{1,3}$};
    \node[state] (l20) at ($(2,-2) + (l13)$) {$\ell_{2,0}$}; % rename to l21
    \node[state] (l31) at ($(-2,-1) + (l13)$) {$\ell_{3,1}$}; 
    \path[->]   
        (l0) edge node[swap]{ $t_0$ } (l10)
        (l10) edge node[swap]{ $t_{1,1}: \tau = x > 0$ } (l21)
        (l10) edge node[swap]{ $t_{4,1}: \tau = x \leq 0$ } (l30)
        (l21) edge node[swap] {$t_{3b,1}$} (l13)
        (l21) edge node {$t_{3a,1}$} (l11)
        (l13) edge[bend right] node {$t_{2}$} (l20)
        (l11) edge[bend right] node[swap] {$t_{2}$} (l20)
        (l20) edge[bend right] node {$t_{1b}$} (l13)
        (l20) edge[bend right] node {$t_{1a}$} (l11)
        (l13) edge node {$t_{4,2}$} (l31)
        % (l2) edge[color=rot-75,bend right=60] node { $t_{2a}:
        % \begin{aligned}&p=0.5\\&\tau=y < z\end{aligned}$ } (l1)
        % (l2) edge[color=rot-75,bend right=80] node[swap] { $t_{2b}:
        % \begin{aligned}&p=0.5\\&\tau=y < z\\&\eta(y)=y+1\end{aligned}$ } (l1)
        % (l2) edge[color=rwth-75,bend left=60] node[swap] {
        % $t_{3a}:\begin{aligned}&p=0.5 \\&\tau=y \geq z\end{aligned}$ } (l1)
        % (l2) edge[color=rwth-75,bend left=80] node {
        % $t_{3b}:\begin{aligned}&p=0.5 \\&\tau=y \geq z\\&\eta(x) = x-1\end{aligned}$ } (l1)
                    ;
\end{tikzpicture}