Given that it is Binary search tree but note that it doesn't said it is balanced.
So, First insertion element is ROOT, in the left sub tree of ROOT, we have all elements which are less than ROOT.
Given Sequence of insertion is 60,25,72,15,30,68,101,13,18,47,70,34,
∴ in the inserting elements 25,15,30,13,18,47,34 are less than 60 and 72,68,101,70 are grater than 60.
No.of Nodes in the left subtree of ROOT = number of nodes less than ROOT = 7.