what is the maximum number of distinct binary tree is possible with 4 nodes? ans is 6 but how? acc to me it should be 14
I can think of no definitions of binary tree and distinct that would produce six distinct binary trees.
There are $14$ plane binary trees, i.e., rooted binary trees in which left and right offspring are distinguished. If left and right offspring are not distinguished, there are only three rooted binary trees:
If you consider unrooted trees, the last two of these are the same: there are only two unrooted binary trees.
If you consider labelled trees, the numbers go up considerably: unrooted the chain graph with four vertices already can be labelled in $12$ ways, so there’s no way to get just six.