\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary {arrows.meta,graphs,graphdrawing} \usegdlibrary {layered}

\begin{document}

\begin{tikzpicture}[nodes={text height=.7em, text width=1.8cm, align=center,
draw=black!20, thick, fill=white, font=\footnotesize},
>={Stealth[round,sep]}, rounded corners, semithick]

\graph [layered layout, level distance=1.5cm, sibling sep=.5em, sibling distance=1.5cm, sweep crossing minimization] {
    "Mission" -> "Task" -> "Skill" -> "Function" -> "Subsystem";

    "Draw a tweet on a board" -> "Writing";
    "Writing" -> { "Write a char at position", "Hold Marker", "Move to position" };
    "Write a char at position" -> { "Move marker on board", "Lift Marker" };
    "Hold Marker" -> "Switch Tools";
    "Move marker on board" -> "SCARA";
    "Lift Marker" -> "End-effector";

    "Draw a tweet on a board" -> "Wiping";
    "Wiping" -> { "Wipe Area", "Hold Wiper", "Move to position" };
    "Hold Wiper" -> "Switch Tools";
    "Move Wiper on Board" -> SCARA;
    "Wipe Area" -> "Move Wiper on Board";

    "Move to position" -> "Move carriage" -> "Carriage";
    "Switch Tools" -> {"End-effector", "SCARA"};
};

 %   \graph [layered layout] {
 %       1 -> 2 -> 3 -> 4;
 %   };



\end{tikzpicture}
\end{document}
