Case 1 is a tree.
Case 2 is a tree.
Case 3 is not a tree.
Case 4 is a tree.
Case 5 is a tree.
Case 6 is a tree.
Case 7 is a tree.
Case 8 is not a tree.
Case 9 is not a tree.
Case 10 is not a tree.
Case 11 is not a tree.
Case 12 is a tree.