in the codes, the p1.root is always null, even if i know the root

I expect the element can be inserted normally, and the function of insert can be valid.

I set a tree structure and set a function “insert” to add elements to the tree.

Can anyone tell me why my root is always null and why my insert method is not assigning a value to the root? Any tips on better design for data structures in Java would also be much appreciated.

public class TreeDemo {
    public static class TreeNode{
        public int val;
        public TreeNode left;
        public TreeNode right;
        public TreeNode(int x){val=x;}
    }
    public static class Tree{
        public TreeNode root;
        public Tree(){
            System.out.println("construct");
            root=null;
        }

        public void Travel(TreeNode root){
            if(root==null){
                return;
            }else{
                Travel(root.left);
                System.out.println(root.val);
                Travel(root.right);
            }
        }

//        public void Delete(int val){
//            if(root==null){
//                System.out.println("wu");
//            }
//            if(root.val==val){
//
//            }
//        }
    }
    public static boolean Search(TreeNode root,int val){
        if(root==null){
            return false;
        }
        if(root.val==val){
            return true;
        }else if(root.val<val){
            return Search(root.left,val);
        }else{
            return Search(root.right,val);
        }
    }
    public static void insert(TreeNode root,int val)
    {
        if(root==null){
            System.out.println("null");
            root=new TreeNode(val);
            System.out.println(root);
            return;
        }
        if(root.val>=val){
            insert(root.right,val);
        }else{
            insert(root.left,val);
        }

    }


    public static void main(String[] args) {
        //System.out.println("hello world");
        Tree p1=new Tree();
        System.out.println(p1.root);
        p1.root=new TreeNode(10);
        System.out.println(p1.root.val);
        System.out.println(p1.root);
        System.out.println("----");
        insert(p1.root,20);
        insert(p1.root,20);
        insert(p1.root,30);
        insert(p1.root,40);
        insert(p1.root,50);
        insert(p1.root,60);
        System.out.println("---------------");

        p1.Travel(p1.root);



    }
}