申論題

7. [20%] The following is a recursive definition of trees:

Now someone modifies the definition and give the following alternative one:
Def 2.
A tree consists of a root, and one or more subtrees T₁, T₂,..., T_k. Also, there is an edge from the root to the root of each subtree.
Can you describe what will happen if we choose the second one as the definition instead? What trees can be generated by the two definitions?