Explanation : If it is to be used for sorting label of left child should be less than the label of the current node. Coming down the tree we get left child of node labeled 10 as the correct slot for 8.
Explanation : It is 12. The tree may be of depth 2 or 1. if the depth is 2, we have 6 possible trees. This is because one of the three nodes A, B, C may be the root and the next level may be one of the remaining two nodes. If the depth is 1, the root may be one of the 3 nodes A, B, C. Corresponding to a root, say A, two trees as possible as this.