I have a Huffman encoding represented as a list in the following manner:

encoding = {{{w, d}, {o, s}}, {{{e, q}, a}, {i, j}}};

This means that w is encoded using $000$, d is encoded using $001$, e is encoded using $1000$, and so on. When I print the list in TreeForm, it looks like this:

Which is pretty fine on its own right, however, I would want to label only the leaves and ignore the internal nodes which say List. How should I go about doing this?