# Multiple overlaid rectangles as TikZ node

I'm trying to create a TikZ flowchart where I need to differentiate between serial and parallel streams. Here's an example with serial to parallel:

I've managed to create a multiple stack of rectangles, but struggle to centre text and it can't be incorporated as a node shape. I could always manually draw it all, but I'm wondering whether there's an easier way to accomplish this? Particularly, is there a way to create a TikZ style with multiples overlaid rectangles that could easily be incorporated into nodes?

Here's my code, which recreates the bottom rectangle, with poorly centred text:

\newcommand{\pstack}[3]{
\draw[fill=white, minimum height=4em] #1 rectangle #2;
\draw[fill=white, minimum height=4em] #1 ++(-0.05,0.05) ++(-0.05,0.05) rectangle +#2;
\draw[fill=white, minimum height=4em, thick] #1 ++(-0.1,0.1) ++(-0.1,0.1) rectangle +#2;
\path #1 -- +#2 node[pos=0.75] {#3};
}
\begin{tikzpicture}[node distance = 2cm, auto]%[scale=.8, z={(-.707,-.3)}]
\pstack{(0,0)}{(2,1)}{some text};
\end{tikzpicture}


You can use double copy shadow from shadows tikz library.

An example:

\documentclass{article}
\usepackage{tikz}
yshift=-1.5ex,draw=black!30},fill=white,draw=black,thick,minimum height = 1cm,minimum
width=2cm},
ordinary/.style = {rectangle,draw,thick,minimum height = 1cm,minimum width=2cm}}
\begin{document}

\begin{tikzpicture}
\node [ordinary] at (0,0) (a) {Some};
\node [multiple,below=3cm of a] (b) {Text};
\draw[-latex] (a) -- coordinate (ab) (b);
\draw (ab) -- ++(0.7,-0.5)coordinate[pos=.3](ab1) coordinate[pos=.6](ab2);
\draw[-latex] (ab1) -- ($(b.north west)!(ab1)!(b.north east)$);
\draw[-latex] (ab2) -- ($(b.north west)!(ab2)!(b.north east)$);
\end{tikzpicture}
\end{document}