source: OniSplit/Dae/Node.cs

using System;
using System.Collections.Generic;

namespace Oni.Dae
{
    internal class Node : Entity
    {
        private TransformCollection transforms;
        private List<Instance> instances;
        private List<Node> nodes;

        public TransformCollection Transforms
        {
            get
            {
                if (transforms == null)
                    transforms = new TransformCollection();

                return transforms;
            }
        }

        public List<Instance> Instances
        {
            get
            {
                if (instances == null)
                    instances = new List<Instance>();

                return instances;
            }
        }

        public IEnumerable<GeometryInstance> GeometryInstances
        {
            get
            {
                if (instances == null)
                    return new GeometryInstance[0];

                return instances.OfType<GeometryInstance>();
            }
        }

        public List<Node> Nodes
        {
            get
            {
                if (nodes == null)
                    nodes = new List<Node>();

                return nodes;
            }
        }
    }
}