SelectWithUnionQuery (children 1)
 ExpressionList (children 1)
  SelectQuery (children 1)
   ExpressionList (children 1)
    Function nested (children 1)
     ExpressionList (children 3)
      Literal Array_[Array_[\'a\'], Array_[\'b\']]
      Literal Array_[Array_[UInt64_1, UInt64_2], Array_[UInt64_3]]
      Literal Array_[Array_[UInt64_4, UInt64_5], Array_[UInt64_6]]
