This script adds "Insert Keys" and "Remove Keys" functionality to the usfca RBTree visualizer.

RBTreePP.user.js

// ==UserScript==
// @name     RedBlackTree++
// @version  1
// @description  This script adds "Insert Keys" and "Remove Keys" functionality to the usfca RBTree visualizer.
// @author       Peter Zhang
// @match        https://www.cs.usfca.edu/~galles/visualization/RedBlack.html
// @grant    none
// ==/UserScript==
//copy everything inside of the setup function below if you want to just paste the code in the console
function setup(){
    const cParent = document.getElementById("AlgorithmSpecificControls");
    const controller = cParent.getElementsByTagName("td");

    function toggleUIOff(){
        controller[8].getElementsByTagName("input")[0].setAttribute("disabled","");
        controller[9].getElementsByTagName("input")[0].setAttribute("disabled","");
        controller[10].getElementsByTagName("input")[0].setAttribute("disabled","");
        controller[11].getElementsByTagName("input")[0].setAttribute("disabled","");
        }
    function toggleUIOn(){
        controller[8].getElementsByTagName("input")[0].removeAttribute("disabled");
        controller[9].getElementsByTagName("input")[0].removeAttribute("disabled");
        controller[10].getElementsByTagName("input")[0].removeAttribute("disabled");
        controller[11].getElementsByTagName("input")[0].removeAttribute("disabled");
            
    }
    
    function insClickHandler(_event) {
        toggleUIOff();
        const keys = insKeysInp.getElementsByTagName("input")[0].value.split(',');
        for (let i = 0; i <= keys.length; i++){
            const disabled = setInterval(function() {
                if (i < keys.length && controller[0].getElementsByTagName("input")[0].disabled == false){
                    controller[0].getElementsByTagName("input")[0].value = keys[i];
                    controller[1].getElementsByTagName("input")[0].click();
                    toggleUIOff();
                    clearInterval(disabled);
                }
                else if (controller[0].getElementsByTagName("input")[0].disabled == false){
                    toggleUIOn();
                }
            }, 100);
        }
    }
    
    function delClickHandler(_event) {
        toggleUIOff();
        const keys = delKeysInp.getElementsByTagName("input")[0].value.split(',');
        for (let i = 0; i <= keys.length; i++){
            const disabled = setInterval(function() {
                if (i < keys.length && controller[2].getElementsByTagName("input")[0].disabled == false){
                    controller[2].getElementsByTagName("input")[0].value = keys[i];
                    controller[3].getElementsByTagName("input")[0].click();
                    toggleUIOff();
                    clearInterval(disabled);
                }
                else if (controller[2].getElementsByTagName("input")[0].disabled == false){
                    toggleUIOn();
                }
            }, 100);
        }
    }

    const insKeysInp = document.createElement("td");
    insKeysInp.innerHTML = "<input type='Text' value='' size='12'>";
    cParent.appendChild(insKeysInp);

    const insKeysBtn = document.createElement("td");
    insKeysBtn.innerHTML = "<input type='Button' value='Insert Keys'>";
    insKeysBtn.addEventListener("click", insClickHandler);
    cParent.appendChild(insKeysBtn);

    const delKeysInp = document.createElement("td");
    delKeysInp.innerHTML = "<input type='Text' value='' size='12'>";
    cParent.appendChild(delKeysInp);

    const delKeysBtn = document.createElement("td");
    delKeysBtn.innerHTML = "<input type='Button' value='Delete Keys'>";
    delKeysBtn.addEventListener("click", delClickHandler);
    cParent.appendChild(delKeysBtn);

    document.getElementById("header").innerHTML = "  \n\t\t\t\t<h1>Red/Black Tree++</h1>\n\t\t\t";
}
window.addEventListener("load", setup, false);