How to draw a full n-ary tree in a "landscape setting" using TikZ?

Question

How would I go about drawing something that looks like this (please excuse the extremely lousy Paint image)

with branches continuing to the right.

I am sorry I cannot provide any exact code, but I am basically clueless as to how I'd do this. I hope you have understanding. Thanks in advance.

Answer 1

This solution uses forest to create the tree. You enter the tree using standard bracket notation.

The following styles are created:

• my node which creates an elliptical node with various attributes - this is used for all main nodes of the tree;
• my label which takes 2 arguments: one specifies position etc. of the label and the other the content - this is used for the small labels on the branches between the main nodes of the tree;
• my top which takes 1 argument: this specifies the content of the rectangular node on top of a main node;
• my label node and my top node specify the appearance etc. of the nodes created using my label={}{} and my top={} respectively.

The nice thing about this is that the tree itself can then be specified very simply and concisely:

[A\\10, my top=5
  [B\\15, my top=5, my label={above left}{7}]
  [C\\18, my top=5, my label={above}{8}]
  [D\\20, my top=5, my label={below left}{6}]
]

\documentclass[tikz, border=5pt]{standalone}
\usepackage{forest}
\usetikzlibrary{shapes.geometric,backgrounds}

\begin{document}
  \forestset{
    my label/.style n args=2{
       edge label={node [my label node, #1] {#2}},
    },
    my top/.style={
      tikz={
        \node [my top node] at (.north) {#1};
      }
    },
  }
  \tikzset{
    my node/.style={shape=ellipse,  draw, inner xsep=15pt, inner ysep=1.5pt, fill=white, thick},
    my top node/.style={draw, anchor=south, on background layer, inner ysep=2pt, yshift=-.5pt, thick, fill=white},
    my label node/.style={auto, midway, font=\sffamily\scriptsize, inner sep=1.5pt},
  }
  \begin{forest}
    for tree={
      grow'=0,
      child anchor=west,
      align=center,
      s sep+=5pt,
      l sep+=10pt,
      font=\sffamily,
      edge=thick,
      thick,
      my node,
    }
    [A\\10, my top=5
      [B\\15, my top=5, my label={above left}{7}]
      [C\\18, my top=5, my label={above}{8}]
      [D\\20, my top=5, my label={below left}{6}]
    ]
  \end{forest}
\end{document}

Answer 2

Like this,

\documentclass[border=10pt]{standalone}
\usepackage{tikz}
\usetikzlibrary{arrows,shapes}
\begin{document}

\tikzstyle{cloud} = [draw, ellipse, node distance=8em,
minimum height=2.75em, minimum width=5.5em]
\tikzstyle{box} = [draw, rectangle, node distance=2.8em]    
\tikzstyle{line} = [draw, -latex']

\begin{tikzpicture}[thick]
%Main nodes
\node[cloud] (a) {\begin{tabular}{c}A \\ 10 \end{tabular}};
\node[right of=a] (invis) {}; %Invisibile node for extra separation 
\node[cloud,right of=invis] (c) {\begin{tabular}{c} C \\ 18 \end{tabular}};
\node[cloud,above of=c] (b) {\begin{tabular}{c}B  \\15 \end{tabular}};
\node[cloud,below of=c] (d) {\begin{tabular}{c}D  \\20 \end{tabular}};
%Extra nodes
\node [draw, box, above of=a] (x) {5};
\node [draw, box, above of=c] (y) {5};
\node [draw, box, above of=b] (z) {5};
\node [draw, box, above of=d] (q) {5};

% Drawing arrows
\path [line] (a) -- node[above] {8} (c);
\path [line] (a) -- node[above] {7} (b);
\path [line] (a) -- node[below] {6} (d);

\end{tikzpicture}
\end{document}

The output of which looks like:

A good tip to drawing in Tikz is to find an example that looks similar and adapt it to your needs.

Edit: If you want more stuff off to the right then just add more nodes with "right of" to position them.