I tried title = {really\\ long title} but it does not work.
One thing that I find is working is to use title = {\parbox{0.4\textwidth}{\centering really long title}}. But this is not as flexible. Is there a way that I can break my title into multiline easily?
node, so Manual/automatic line breaks and text alignment in TikZ nodes applies here. You can set the properties of the title node usingtitle style={<options>}. – Jake Dec 16 '14 at 21:57