insert.tex

\documentclass[margin=0.5cm]{standalone}

\usepackage{array}
\usepackage{amsmath}

%
% Cooper Pierce <cppierce@andrew.cmu.edu>
%
% For use in the book,
%   1. compile with latexmk,
%   2. use dvisvgm
% E.g., latexmk insert
%   && dvisvgm --no-fonts --clipjoin --bbox=papersize insert
%   && mv insert-1.svg insert.svg
% (for whatever reason my version of pdflatex makes a two page dvi)
%
%

\usepackage{tikz}
\usetikzlibrary{arrows}
\usepackage{forest}

\begin{document}
    \pagecolor{white}
    \tikzset{%
        /forest,
        forest node/.style={circle, inner sep=0pt, text centered},
        arn n/.append style={
            text=white,
            font=\sffamily\bfseries,
            draw=black,
            fill=black,
            text width=1.5em,
        },
        arn r/.append style={%
            text=white,
            font=\sffamily\bfseries\tiny,
            draw=red,
            fill=red,
            text width=1.5em,
        },
    }

    \forestset{%
        default preamble={
            for tree={
                font=\sffamily,
                forest node,
                edge path={
                    \noexpand\path[color=black, -stealth', \forestoption{edge}]
                    (!u.parent anchor) -- (.child anchor)\forestoption{edge label};
                },
                l sep+=.25cm,
                s sep+=.25cm,
                fit=band,
            }
        }
    }
    \begin{tabular}{m{0.8cm} m{2em} m{0.5cm} m{2em} m{1.5cm}}
        Empty
    &
        \( \xrightarrow[a\,\mapsto\,2]{\text{ins.}} \)
    &
        \begin{forest}
            [a\,:\,2, arn r]
        \end{forest}
    &
        \( \xrightarrow[b\,\mapsto\,3]{\text{ins.}} \)
    &
        \begin{forest}
            [a\,:\,2, arn r,
                [,phantom]
                [b\,:\,3, arn r]
            ]
        \end{forest}
    \end{tabular}
\end{document}