ProgramNode(0...6)(
  [],
  StatementsNode(0...6)(
    [CallNode(0...6)(
       nil,
       nil,
       (0...1),
       (1...2),
       ArgumentsNode(2...4)([InstanceVariableReadNode(2...4)()]),
       (5...6),
       nil,
       0,
       "a"
     )]
  )
)
