complete a data structure

I NEED TO COMPLETE A DATA STRUCTURE TO THE FOLLOWING CODE. THE DATA SHOULD BE LIKE A TREE WHERE "A" IS THE FIRST NODE AND HAS TWO CHILD, AND EACH CHILD HAS TWO AS WELL. CHILD COULD BE "NIL". THIS PROGRAM IS WRITTEN IN STANDARD ML LANGUAGE. AND MUST BE COMPLETED IN THE SML AS WELL. --------------------------------------------- fun Lof(x: int*char list*int list) = length(#2 x)-1; fun getlist(x: int*char list* int list) = #2 x; fun position(item, index, L) = if index