Building a `forest` tree :-) step by step

Question

I would like to get the following steps using beamer. I would need some hints to start my coding...

Here is the code of the tree.

\documentclass[12pt]{article}
\usepackage{forest}
\begin{document}
\begin{forest} 
  for tree = {math content},
  where n children = 0 {tier = word} {}
  [243
    [3   [3^1]]
    [81
      [9   [3^2]]

      [9   [3^2]]
    ]
  ]
  \path (!11.base east)  -- (!211.base west) node[midway, anchor=base]{$\times$};
  \path (!211.base east) -- (!221.base west) node[midway, anchor=base]{$\times$};
\end{forest}
\end{document}