Split node padding when using align in TikZ

Consider the following code:

\documentclass{article}

\usepackage{tikz}
\usetikzlibrary{shapes,positioning,fit}

\begin{document}

\begin{tikzpicture}
\node[draw, rectangle split, rectangle split parts=2]{
x y%
\nodepart{two}{%
\tikz \node[draw, rectangle] {bubble \\ gum};%
}
};
\end{tikzpicture}

\vspace{2em}

\begin{tikzpicture}
\node[align=center, rectangle split part align={center, left}, draw, rectangle split, rectangle split parts=2]{
x y%
\nodepart{two}{%
\tikz \node[draw, rectangle] {bubble \\ gum};%
}
};
\end{tikzpicture}

\vspace{2em}

\begin{tikzpicture}
\node[align=left,draw, rectangle split, rectangle split parts=2]{
x y%
\nodepart{two}{%
\tikz \node[draw, rectangle] {bubble \\ gum};%
}
};
\end{tikzpicture}

\end{document}


It produces the following:

In the first example, the inner node is correctly nested in the center of the outer one. However, line breaks in the inner node content are ignored.

Adding align=center or align=left to the options of the outer node results in the line breaks being respected, but the inner node is not centered any more. I don't understand why this is happening.

How can I get the desired behaviour: line breaks are displayed and the inner node is centered within the outer one?

-

Like this ?

\documentclass{article}

\usepackage{tikz}
\usetikzlibrary{shapes,positioning,fit}

\begin{document}

\begin{tikzpicture}
\node[rectangle split part align={center, left}, draw, rectangle split, rectangle split parts=2]{
x y%
\nodepart{two}{%
\tikz \node[align=center, draw, rectangle] {bubble \\ gum};%
}
};
\end{tikzpicture}

\vspace{2em}

\begin{tikzpicture}
\node[draw, rectangle split, rectangle split parts=2]{
x y%
\nodepart{two}{%
\tikz \node[align=left,draw, rectangle] {bubble \\ gum};%
}
};
\end{tikzpicture}

\end{document}


-