如何将嵌套字典中的值映射到dataframe中的多个列

import pandas as pd

data = {
    'A': {'a': 1, 'b': 2, 'c': 3},
    'B': {'a': 4, 'b': 5, 'c': 6},
    'C': {'a': 7, 'b': 8, 'c': 9}
}

df = pd.DataFrame(data)

   A  B  C
a  1  4  7
b  2  5  8
c  3  6  9

import pandas as pd

data = {
    'A': {'a': [1, 2], 'b': [3, 4], 'c': [5, 6]},
    'B': {'a': [7, 8], 'b': [9, 10], 'c': [11, 12]},
    'C': {'a': [13, 14], 'b': [15, 16], 'c': [17, 18]}
}

df = pd.DataFrame(data)

    A   B   C
a  [1, 2]  [7, 8]  [13, 14]
b  [3, 4]  [9, 10] [15, 16]
c  [5, 6]  [11, 12] [17, 18]