Two types of sub-enumerator

I'm using custom enumerators for work packages and tasks:

\newlist{WP}{enumerate}{2}
\setlist[WP,1]{label*=WP\arabic*.,ref=\arabic*}


which results in the following output:

WP1. Foo
WP2. Another


I'd like to be able to put another kind of sub-enumerator there, with the numbering restarting, such as:

WP1. Foo
Deliverable 1.1. Report on Bar and Baz
WP2. Another
Deliverable 2.1. Report on Foobar


Not ideal, but I found a way of doing it within the enumerate itself:

 \begin{WP}
\item Foo
\begin{WP}
\item Bar
\item Baz
\end{WP}
\begin{enumerate}[label=D\arabic{WPi}.\arabic*,ref=\arabic{WPi}.\arabic*]
\item Report on Bar and Baz
\end{enumerate}
\end{WP}