A Confusing Tree Question

Where is this formula used?

left_tree (data) <= node (data) <= right_tree (data)

Binary tree or BST or AVL Tree or Heap

What formula ???We use recursion to solve problems .
Please elaborate

root->data means root data

root->left->data means root left child data
root->right ->data means root right child data

// A binary tree node

struct Node
    int data;
    struct Node* left;
    struct Node* right;
    Node(int x){
        data = x;
        left = right = NULL;

answer is BST …Avl tree is a types for binary tree that balances itself