C++ Tree node ,when g++ compile multiple cpp files should list them respectively

//TreeNode.h
#include <iostream>
using namespace std;

class TreeNode
{
public:
    int val;
    TreeNode *left;
    TreeNode *right;
    TreeNode *NewTreeNode(int keyValue);
    void treeNode7();
};

//TreeNode.cpp
#include "TreeNode.h"
TreeNode* TreeNode::NewTreeNode(int keyValue)
{           
    //Create a new node
    TreeNode *node=new TreeNode;

    //assign a value
    node->val=keyValue;

    //Initialize Left and Right pointer
    node->left=NULL;
    node->right=NULL;
    return node;
}

void TreeNode::treeNode7()
{
    TreeNode *root=NewTreeNode(1);
    root->left=NewTreeNode(2);
    root->right=NewTreeNode(3);
    root->left->left=NewTreeNode(4);
    root->left->right=NewTreeNode(5);
    root->right->left=NewTreeNode(6);
    root->right->right=NewTreeNode(7);
    
    cout<<"root->val="<<root->val<<endl;
    cout<<"root->left->val="<<root->left->val<<endl;
    cout<<"root->left->left->val="<<root->left->left->val<<endl;
    cout<<"root->left->right->val="<<root->left->right->val<<endl;
    cout<<"root->right->left->val="<<root->right->left->val<<endl;
    cout<<"root->right->right->val"<<root->right->right->val<<endl;
}
 

Compile via

g++ -g -std=c++2a -I. h1.cpp TreeNode.cpp -o h1 -luuid

When compile multiple cpp files ,please add them respectively in the command as above  

Run ./h1