binary search tree - BST insertion with C++ -

i created function insert data bst , works fine. used "pass reference" , value of "head" supposed change after each insertion. however, found "head" pointing first value inserted. here explain causes "head" point first data inserted?

void insert(node *&head, int val){ if(head == null){     head = newnode(val); } else{     if(val <head->data)         insert(head->left,val);     else         insert(head->right,val); } } 

that how function should work, head should never change or lose track of tree root.

as long have head pointing @ root, have access whole tree.

the reason why value not changing is, when writing insert(head->left,val);

you not assigning new value head, passing reference left child next function call.