code: def get_nodes(self):
          
          nodes = []
          for age, level in enumerate(self.nodes):
              nodes.append([])
              for node in level:
                  nodes[age].append(node.get_tuple())
          return nodes
docs: Get the tree nodes as list.
  
          Returns:
              list: A 2d-list holding the grown nodes coordinates as tupel for every age.
                  Example:
                  [
                  [(10, 40)],
                  [(20, 80), (100, 30)],
                  [(100, 90), (120, 40), ...],
                  ...
                  ]