(A 1), (B 2), (C 4), ...
Tree sketch (n=5):

      *
   /     \
(E 16)    *
       /     \
    (D 8)     *
           /     \
        (C 4)     *
               /     \
            (B 2)   (A 1)

tree sketch (n=10):
       *
    /     \
(J 512)   *
       /     \
   (I 256)    *
           /     \
       (H 128)    *
               /     \
            (G 64)    *
                   /     \
                (F 32)    *
                       /     \
                    (E 16)    *
                           /     \
                        (D 8)     *
                               /     \
                            (C 4)     *
                                   /     \
                                (B 2)   (A 1)

The most frequent symbol always requires exactly 1 bit.
The two least frequent symbols will always require exactly n-1 bits.