I don't understand how to move portions of a tree

问题

My goal is to create a BST that: when I insert a node I insert it at the root, if the element to insert already exists move the existing element to the root. If you remove a node, move the father of that node to the root.

class BSTNode {

BSTNode left = null;
BSTNode rigth = null;
int data = 0;

public BSTNode() {
    super();
}

public BSTNode(int data) {
    this.left = null;
    this.rigth = null;
    this.data = data;
}

@Override
public String toString() {
    return "BSTNode [left=" + left + ", rigth=" + rigth + ", data=" + data + "]";
}

}


class BinarySearchTree {

BSTNode root = null;

public BinarySearchTree() {

}

public void insert(int data) {
    BSTNode node = new BSTNode(data);
    if (root == null) {
        root = node;
        return;
    }else{

        BSTNode currentNode = root;
        BSTNode parentNode = null;



            if (currentNode.data == data)
                return;

            if (currentNode.data > data) {
                parentNode = node;

                BSTNode existing = searchNode(data);

                if (existing != null){
                    parentNode = existing;
                    parentNode.rigth = currentNode;
                }else{
                    parentNode.rigth = currentNode;
                }        
            } else {
                parentNode = node;

                BSTNode existing = searchNode(data);

                if (existing != null){

                    parentNode = existing;
                    parentNode.left = currentNode;
                }else{
                    parentNode.left = currentNode;
                }
            }
            root = parentNode;
        }
    }


public BSTNode searchNode(int data) {
    if (empty())
        return null;
    return searchNode(data, root);
}

public BSTNode searchNode(int data, BSTNode node) {
    if ((node.left != null && node.left.data == data) || (node.rigth != null && node.rigth.data == data)) {
        if (node.left.data == data){
            BSTNode existing = node.left;
            node.left = null;
            return existing;
        }
        if(node.rigth.data == data){
            BSTNode existing = node.rigth;
            node.rigth = null;
            return existing;
        }
        else if (node.data > data)
            return searchNode(data, node.left);
        else if (node.data < data)
            return searchNode(data, node.rigth);  
    }
    return null;
}

I haven't dealt with the Delete yet. I'm stuck at the insert function.

My idea here was: replace the old root with the new one and hook the old root to the left of the new one, if it is smaller, or to the right if it is larger. Also if it is the old root is smaller than the new one, look for the first largest element of the new root on the right branch of the old root, and move it by hooking it as the right branch of the new root. In reverse if it is bigger.

But I'm not capable. Can anyone help me? Maybe before closing the "question" I would also need some advice on the delete operation.

来源：https://stackoverflow.com/questions/61069856/i-dont-understand-how-to-move-portions-of-a-tree