Why do you have the tree and the animal in the same family to begin with?
Events can still be added independantly from each other just as you described by putting "tree.x" this will not affect your animals in any way.
Only events added to the family will be applied to both the animal and the tree.
And if you must know, you could add an instance variable to both the tree and the animal and call it "test".
For the animal "test" will be 1 and for the tree "test" will be 0.
This way you can check the instance variable to see which instant it actually is.
I hope this helps you in the general direction you would like to go.