private List<T> DoSearch(
    in RectangleF boundingBox, 
    ContainmentType ctype = ContainmentType.Intersects, 
    int maxLevel = int.MaxValue)
{
    if (ctype == ContainmentType.Intersects)
    {
        if (!boundingBox.Containment(Root.Envelope, ctype) || maxLevel < 1)
            return [];
    }

 var intersections = new List<T>();
    var queue = new Queue<Node>();
    queue.Enqueue(Root);

    while (queue.Count != 0)
    {
        var item = queue.Dequeue();

        if (item.IsLeaf)
        {
            foreach (var i in item.Items)
            {
                if (boundingBox.Containment(i.Envelope, ctype))
                    intersections.Add((T)i);
            }
        }
        else
        {
            if (maxLevel-- > 0)
            {
                foreach (var i in item.Items)
                {
                    if (boundingBox.Containment(i.Envelope, ctype))
                        queue.Enqueue((Node)i);
                }
            }
        }
    }

    return intersections;
}