希望在嵌套的项目化环境中添加垂直线来分隔头部级别，如图所示。
有一个类似的问题这里。但我想保留如图所示的项目符号。
以下是 MWE：
\documentclass{article}
\usepackage{graphicx} % Required for inserting images
\begin{document}
\section{Introduction}
\begin{itemize}
\item Head Level 1: some text some text some text some text some text some text some
text some text some text some text some text some text some text
\begin{itemize}
\item Sub-level 1: some text some text some text some text some text some text some text some text some text some text some text some text
\begin{itemize}
\item subsub-level 1: some text some text some text some text some text some text some text some text some text some text some text
\end{itemize}
\end{itemize}
\item Head Level 2: some text some text some text some text some text some text some text some text some text some text some text some text some text
\begin{itemize}
\item Sub-level 2: some text some text some text some text some text some text some text some text some text some text some text some text some text
\begin{itemize}
\item subsub-level 2: some text some text some text some text some text some text some text some text some text some text some text some text some text
\end{itemize}
\end{itemize}
\end{itemize}
\end{document}
