input: Write a python function to generate the next level of nodes in a binary tree.
  assert generateNextLevel([Node(1, Node(2), Node(3))]) == [Node(2), Node(3)]
  assert generateNextLevel([Node(1, None, Node(3))]) == [Node(3)]
  assert generateNextLevel([Node(1, Node(2, Node(4)), Node(3))]) == [Node(2), Node(3)]
output: class Node:
      def __init__(self, value=0, left=None, right=None):
          self.value = value
          self.left = left
          self.right = right
  
  def generateNextLevel(nodes):
      next_level = []
      for node in nodes:
          if node.left is not None:
              next_level.append(node.left)
          if node.right is not None:
              next_level.append(node.right)
      return next_level