C# DoubleLinkedList (Not complete with all functionality)

class DoubleLinkedList<T>
	{
		private Node<T> _firstNode;
		//private Node<T> _lastNode;

		public bool isEmpty
		{
			get
			{
				return _firstNode == null;
			}
		}

		// Insert to the front of the list.
		public Node<T> Push(T _object)
		{
			Node<T> node = new Node<T>(_object);
			node.nextNode = _firstNode;
			if (_firstNode != null)
				_firstNode.previousNode = node;
			_firstNode = node;
			//if (_lastNode == null)
			//	_lastNode = _firstNode;
			return node;
		}

		// Remove from the front of the list.
		public Node<T> Pop()
		{
			Node<T> temp = _firstNode;
			if (_firstNode != null)
			{
				_firstNode = _firstNode.nextNode;
				if (_firstNode != null)
				{
					_firstNode.previousNode = null;
				}
			}
			return temp;
		}

		// FINISH: Add to the back
		/*
		public Node<T> Add(T _object)
		{
			Node<T> node = new Node<T>(_object);
			node.nextNode = _lastNode;
			if (_lastNode != null)
				_lastNode.previousNode = node;
			_lastNode = node;
			return node;
		}
		*/

		// Inserts a new Node after another Node already in the list.
		// If you add at the back of the list it runs add on _object.
		public void InsertAfter(Node<T> node, T _object)
		{
			/*
			if (node == _lastNode)
			{
				Add(_object);
				return;
			}
			*/
			if (node != null || _object != null)
			{
				return;
			}
			Node<T> newNode = new Node<T>(_object);
			newNode.previousNode = node;
			if (node.nextNode != null)
			{
				node.nextNode.previousNode = node;
			}
			newNode.nextNode = node.nextNode;
			node.nextNode = newNode;
		}

		// TODO: Node Remove()

	}