\documentclass[11pt]{article}
\usepackage{multirow}
\begin{document}

\begin{table}[ht]
\begin{center}
\begin{tabular}{ccc}
    \hline
    \multirow{2}{*}{Outer index 1} & Inner index 1.1\\
    & Inner index 1.2\\
    \hline
    \multirow{2}{*}{Outer index 2} & Inner index 2.1\\
    & Inner index 2.2\\
    \hline
    \multirow{6}{*}{Outer index 3} &  Inner index 3.1\\
    &Inner index 3.2\\
    &Inner index 3.3\\
    &Inner index 3.4\\
    &Inner index 3.5\\
    &Inner index 3.5\\
    &Inner index 3.6\\
    \hline
\end{tabular}
\end{center}
\label{tab:multicol}
\end{table}

\end{document}