 % This file is public domain
 % If you want to use arara, you need the following directives:
 % arara: pdflatex: { synctex: on }
 % arara: makeglossaries
 % arara: pdflatex: { synctex: on }
\documentclass{article}

\usepackage[colorlinks]{hyperref}
\usepackage[style=tree]{glossaries}

\makeglossaries

\renewcommand*{\glsentryfmt}{%
  \glsgenentryfmt
  \ifglsused{\glslabel}{}{\space (\glsentrysymbol{\glslabel})}%
}

\newglossaryentry{distance}{name=distance,
description={The length between two points},
symbol={km}}

\begin{document}

First use: \gls{distance}. Next use: \gls{distance}.

\printglossaries

\end{document}
