Find a formula for the total number of calls occurring during the insertion of n elements into an initally empty set. Assume that the insertion process fills up the binary search tree level-by-level. Leave your answer in the form of a sum.

procedure INSERT(x: elementtype; var A: SET) begin if A- nil then begin new(A); A1.element := x; A.leftchild := nil; AT.rightchild := nil end else if x AT.element then INSERT(x, AT.rightchild) end