slow run time

gistfile1.txt

var kthSmallest = function(root, k) {
    var result = [];
    var search = (node) => {
        if (node.val !== null) {
            result.push(node.val);
        }
        if (node.left) {
            search(node.left);
        }
        if (node.right) {
            search(node.right);
        }
        if (node.right === null && node.left === null) {
            return;
        }
    };
    
    search(root);
    console.log(result);
    return result.sort((a,b) => {
        return a - b;
    })[k-1];
    
};