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.

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<code>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);

}

}

</code>

<code>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); } } </code>

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);



    }
}