[Tex/LaTex] Beamer: Change only several bullets in the list

Question

I would like to change the bullets in the second itemize to arrows.

\begin{alertblock}{The Aim of this Research} 
    \begin{itemize}
        \item Item 1
        \item Item 2
            \begin{itemize}
                \item Item 2-1
                \item Item 2-2
            \end{itemize}
    \end{itemize} 
\end{alertblock}

Form above, I would like to make:

・Item 1 
・Item 2
   => Item 2-1  (change bullet to arrow)
   => Item 2-2

I've tried inserting \renewcommand{\labelitemii}{$\rightarrow$} before and after the second \begin{itemize} and the solution in this question, but they don't work.

Answer 1

You can define your bullet symbols direct in the itemization:

\begin{itemize}
   \item[$\rightarrow$] Item 1
\end{itemize}