k in t

function kthLargestInBST(t, k) {
  var check = function (value) {
    k--;
    if (k === 0) {return value;}
    else {return false;}
  }

  var loop = function (node) {
    if (!node) {return false}
    return loop(node.left) || check(node.value) || loop(node.right)
  }
  return loop(t);
}