Why I can't assign variables with constructor and get the wrong value from it?

I would like to implement a BST in C++, but I found that the integer variable "val" I pass in the constructor "Node()" seem not to work properly.
P.S. I am a totally newbie to this language, and here is my code

#include<iostream>
using namespace std;


class Node{

    public:
        int val;
        Node *left;
        Node *right;
        // the constructor
        Node(int val){
            val = val;
            left = nullptr;
            right = nullptr;
        }
};

class BST{
    public:
        Node *root;
        BST(){
            root = nullptr;
        }
        void insert(int val);
};

void BST::insert(int val){
    if (root == nullptr){
        root = new Node(val);
        cout << root->val << endl; // output: 40580256(this number changes every time I run the code) 
        delete root;
    };
    
    if (root->val == val){
        cout<<"The value: " << val << " is duplicated!" << endl;
    }

}

int main() {
    BST bst;
    Node a = Node(10); // output: 8
    cout << a.val << endl;;
    bst.insert(8);
    
    
    return 0;
}

It only works when I directly assign the variable "val" to root.val instead of using constructor to assign.

>Solution :

The reason why you’re having a problem is outlined in the comments, but, stylistically, it’s better to do this:

class Node{

    public:
        int val;
        Node *left = nullptr;
        Node *right = nullptr;
        // the constructor
        Node(int val) : val (val) { }
};

Now, nothing can go wrong.