scratch.tex

\documentclass[border=5mm]{standalone}

\usepackage{tikz}

\begin{document}

\begin{tikzpicture}[x=1mm,y=-1mm]%
  \draw (10,0) -- (10,10);
  \draw (30,0) -- (30,10);
  \draw (50,0) -- (50,30);
  \draw (70,0) -- (70,50);
  \fill[red] (0,10) rectangle (40,20);
  \node at (20,15) {decide};
  \draw (10,20) -- (10,50);
  \node[anchor=east] at (10,25) {yes};
  \node[anchor=east] at (30,25) {no};
  \draw (30,20) -- (30,30);
  \fill[red!50] (20,30) rectangle (60,40);
  \draw (30,40) -- (30,50);
  \draw (50,40) -- (50,70);
  \fill[red] (0,50) rectangle (40,60);
  \node at (20,55) {join};
  \fill[red] (60,50) rectangle (80,60);
  \draw (20,60) -- (20,70);
  \draw (70,60) -- (70,70);
\end{tikzpicture}

\end{document}