Segment tree implementation with pointer in C++

pointerSegTree.cpp

#include <bits/stdc++.h>

using namespace std;
typedef long long ll;

class SegmentTree {
   private:
    struct Node {
        Node* _left;
        Node* _right;
        pair<ll, ll> range;
        ll value = 0;

        Node(ll l, ll r) {
           _left = _right = nullptr;
            range = {l, r};
        }

        ~Node() {
            delete _left;
            delete _right;
        }

        Node* left() {
            auto [l, r] = range;

            if (l == r) {
                return nullptr;
            }

            return _left = (_left == nullptr ? new Node(l, (l + r) / 2) : _left);
        }

        Node* right() {
            auto [l, r] = range;

            if (l == r) {
                return nullptr;
            }

            return _right = (_right == nullptr ? new Node((l + r) / 2 + 1, r) : _right);
        }
    };

    Node* root = nullptr;

    void _update(Node* cur, ll i, ll x) {
        auto [l, r] = cur->range;

        if (!(l <= i && i <= r)) {
            return;
        }

        if (l == r) {
            cur->value = x;
            return;
        }

        _update(cur->left(), i, x);
        _update(cur->right(), i, x);

        cur->value = cur->left()->value + cur->right()->value;
    }

    ll _query(Node* cur, ll a, ll b) {
        if (cur == nullptr) {
            return 0;
        }

        auto [l, r] = cur->range;

        if (r < a || b < l) {
            return 0;
        }

        if (a <= l && r <= b) {
            return cur->value;
        }

        return _query(cur->left(), a, b) + _query(cur->right(), a, b);
    }

   public:
    SegmentTree(ll n) {
        root = new Node(0, n - 1);
    }

    ~SegmentTree() {
        delete root;
    }

    void update(ll i, ll x) {
        _update(root, i, x);
    }

    ll query(ll l, ll r) {
        return _query(root, l, r);
    }
};

int main() {
    SegmentTree tree(8);

    for(ll i = 0; i < 8; i++) {
        tree.update(i, i + 1);
    }

    cout << tree.query(0, 3) << '\n'; // 10
    cout << tree.query(1, 5) << '\n'; // 20
}