C++ :: How To Insert Item Into Binary Tree

I am trying to write a function that inserts an item into this binary tree in C++.

template <typename T>
struct BTree {
T val;
BTree<T>* left;
BTree<T>* right;
BTree(T v, BTree<T>* l=nullptr, BTree<T>* r=nullptr) :
val(v), left(l), right(r) {}
};

Here's my attempt.

template <typename T>
void insert(BTree<T>* tree, T item) {
if (tree == nullptr) {
tree = new BTree<T>(item);
} else if (item < tree->val) {
insert(tree->left, item);
} else {
insert(tree->right, item);
} }

I think this function may not be working because I am modifying `tree`, which is a local variable. How do I actually modify the current pointer that `tree` represents, not just `nullptr`?