public static T Find<T>(
    this IEnumerable<T> source,
    Func<T, IEnumerable<T>> childrenSelector,
    Predicate<T> condition)
{
    T t = default(T);
    foreach (T item in source)
    {
        if (condition(item))
        {
            return item;
        }

        t = childrenSelector(item).Find<T>(childrenSelector, condition);

        if (!Equals(t, default(T)))
        {
            return t;
        }
    }
    return t;
}