If if you have several projects in one window, you mean the presence of several directories located in different places of your system immediately in the sidebar tree, then yes, you can do it.
-a flag means add to the last focused window instead of opening in a new window).
EDIT
Even easier.
Open the first project. Go to (in the menu above)
Project → Add folder to project
Sergey Telshevsky Sep 08 '14 at 9:40 2014-09-08 09:40
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