Explain EXPLAIN QUERY TREE (children 1)
 SelectWithUnionQuery (children 1)
  ExpressionList (children 1)
   SelectQuery (children 2)
    ExpressionList (children 1)
     Function sum (children 1)
      ExpressionList (children 1)
       Function plus (children 1)
        ExpressionList (children 2)
         Literal UInt64_2
         Identifier uint64
    TablesInSelectQuery (children 1)
     TablesInSelectQueryElement (children 1)
      TableExpression (children 1)
       TableIdentifier test_table
