You dont need to connect them to each other. Connect leaves signals to leaves themselves, and You can recognize collision inside the function :
func on_area_enetered(area) :
if area is Player :
there are many methods to recognize collision.
iskeyword is for checking classes, meaning if You introduced Player as
classname Player. But You can also check for
has_method() and so on.
Advanced sollution for this problem would be to connect all signals within autoloaded script.