Enumeration is to list all possible results. You can write all the results directly.

For example, 1, 2, 3 can form two numbers: 12, 13, 23, 2 1, 3 1, 32.

The tree method lists all possible results by drawing a tree diagram.

List method is to list all possible results by list.

The answer to the same question you did is different from that of the tree method. You must have missed some possible results.