Given a binary tree and a key, insert the key into the binary tree at first position available

binsert.js

const insert = (tree, value) => {
  const plug = [];
  plug.push(tree);

  while(plug.length){
    const elem = plug.shift();

    if(!elem.left) {
      elem.left = node(value);
      break;
    }else{
      plug.push(elem.left);
    }

    if(!elem.right){
      elem.right = node(value);
      break;
    }else{
      plug.push(elem.right);
    }
  }
}

insert(tree, 12);