I have got a graph theory question from a friend as follows:
It is a tree as shown below rooted at "a". And asks me to find the number of subtrees it has.
I have found 5 subtrees as marked in red cirles. He says, it is 6. Am I missing any possible subtree, which by definition is a subtree?
Updated: Definition of subtree -
Subtree is a non-empty subgraph satisfying the following condition: For any vertex x, if x belongs to subtree P, then the parent of x also belongs to P. Note that each subtree contains the root.