Expected ')' to match this '(' when adding & to function prototype : I'm writing a recursive bst insert function and I recognized that I was modifying a copy of the struct.

So I changed the prototype of the function from this: ```void BSTRecursiveInsert(BSTNode* tree, DataObject* elem)``` to this: ```void BSTRecursiveInsert(BSTNode*& tree, DataObject* elem)``` but I get the compiler error I wrote as question title. What am I missing?