JSFiddle - React, Tailwind, and code Playground

JavaScript

var obj = {
    id: 23,
    name: 'Test1',
    children: [{
         id: 24,
         name: 'Test2',
         children: []
    },{
         id: 25,
         name: 'Test2',
         children: []
    }],
};

var objToBePushed = {
    id: 26,
    name: 'Test3',
    children: [{
         id: 27,
         name: 'Test4',
         children: []
    }]
};

function findNode(nodeId, json, node){
    if(node.id == nodeId){
        node.children.push(json);
    }
    else{
        
        for(var i=0; i<node.children.length; i++){
            findNode(nodeId, json, node.children[i]);
        }
    }
}

findNode(24, objToBePushed, obj);
console.log(obj);