# How to create child PDF bookmarks in index for each index letter

I have a rather lengthy index to my document. I have a bookmark so I can quickly get to the index, but I'd like child bookmarks for each letter of the alphabet so I can go to that section of the index directly. I am currently using the imakeidx package for generating my index, but I couldn't find any package options allowing me to create the child bookmarks.

Any suggestions?

Example file:

\RequirePackage{filecontents}
% File \jobname.mst is overwritten, if package filecontents is loaded!
\begin{filecontents*}{\jobname.mst}
\end{filecontents*}

\documentclass{article}
\usepackage{hyperref}
\usepackage{bookmark}

\belowpdfbookmark{#1}{#1}%
}

\usepackage{imakeidx}
\makeindex

\begin{document}
Hello\index{hello} world\index{world}!

\cleardoublepage
\pdfbookmark{\indexname}{index}
\printindex
\end{document}


Makeindex automatically looks for a file \jobname.mst for style definitions. There the headings can be configured. The example inserts macro \IndexHeading, which creates a bookmark below the current level.