trees in tex with tikz

trees.tex

\documentclass[german,11pt]{article}
\usepackage{tikz}
\usepackage{pgfplots}

\usepgfplotslibrary{dateplot}

\usetikzlibrary{arrows}
\usetikzlibrary{positioning}
\usetikzlibrary{external}
\usetikzlibrary{graphs,quotes,graphdrawing,arrows.meta,backgrounds}
\usegdlibrary{layered,trees}
\usetikzlibrary{arrows.spaced,arrows}
\usetikzlibrary{positioning}

\begin{document}


\tikzset{
  graphs/graph/.style={
    nodes={circle, draw, minimum size=7mm},
    edges={-{Stealth[round,sep]},semithick},
  }
}

\def\mywidth{5mm}
\begin{tikzpicture}[
    semithick,
    > = spaced stealth',
    box/.style={
      draw, thick, black, rectangle,
      minimum height = 5mm,
      minimum width  = \mywidth,
    },
    node distance=0pt,
  ]
  
  \begin{scope}[yscale=1.4]
    \node (root) at (-1,0) {\textsc{root}};

    \foreach \x/\y/\a/\b/\c [count=\d] in {%
      1/0/1//,%
      0/-1/2/0/,%
      2.5/-1/2//1,%
      1/-2/3/0/1,
      1/-3/4/5/6%
    }
    {
      \coordinate (x) at (\x,\y);
      \node [box] at (                   x) (box \d a) {\a};
      \node [box] at ([xshift=\mywidth]  x) (box \d b) {\b};
      \node [box] at ([xshift=2*\mywidth]x) (box \d c) {\c};
    }
    
    \draw (root)   edge[->]  (box 1a);
    \draw [out=-90,in=90]
      (box 1b.center) edge [->] (box 2c)
      (box 1c.center) edge [->] (box 3b)
      (box 2c.center) edge [->] (box 4b)
      (box 3b.center) edge [->] (box 4c)
    ;
  \end{scope}
  
  \foreach \start in {box 1b,box 1c,box 2c,box 3b}
    \fill (\start.center) circle[radius=2pt];
  
\end{tikzpicture}

\begin{tikzpicture}
  \graph [graph,tree layout] {
    / -> {
      / -> {
        /,
        / -> {
          /, /
        },
        /,
        ,
        / -> /
      },
      / -> {
        /, /
      }
    }
  };
\end{tikzpicture}

\end{document}