How to add Unity as an alternative desktop to Xubuntu 14.10

[Gordonbp531]

I currently have Xubuntu 14.10 on my Acer E3, and would like to have the option of switching to Unity.
I tried

sudo apt-get install unity but when I go to log back in, there's no option to choose Unity.
Presumably I've missed something vital...;)

[deadflowr]

I believe installing unity pulls in all the needed dependencies and extra packages except one, ubuntu-session.
Install that and I think it should add unity to the login options.