this function is very simple we pass in node if the node contains an operandthen we simply return that value if we get an operatorhoweverthen we perform the operation that the operator representson the node' two children howeversince one or more of the children could also contain either operators or operandswe call the calc(function recursively on the two child nodes (bearing in mind that all the children of every node are also nodesnow we just need to pop the root node off the stack and pass it into the calc(function and we should have the result of the calculationroot stack pop(result calc(rootprint(resultrunning this program should yield the result which is the result of ( ( balancing trees earlierwe mentioned that if nodes are inserted into the tree in sequential orderthen the tree behaves more or less like listthat iseach node has exactly one child node we normally would like to reduce the height of the tree as much as possibleby filling up each row in the tree this process is called balancing the tree there are number of types of self-balancing treessuch as red-black treesaa treesand scapegoat trees these balance the tree during each operation that modifies the treesuch as insert or delete there are also external algorithms that balance tree the benefit of these is that you wouldn' need to balance the tree on every single operationbut could rather leave balancing to the point when you need it heaps at this pointwe shall briefly introduce the heap data structure heap is specialization of tree in which the nodes are ordered in specific way heaps are divided into max and min heaps in max heapeach parent node must always be greater than or equal to its children it follows that the root node must be the greatest value in the tree min heap is the opposite each parent node must be less than or equal to both its children as consequencethe root node holds the lowest value