Explain EXPLAIN QUERY TREE (children 2)
 Set
 SelectWithUnionQuery (children 1)
  ExpressionList (children 1)
   SelectQuery (children 2)
    ExpressionList (children 2)
     Function quantile (children 2)
      ExpressionList (children 1)
       Identifier b
      ExpressionList (children 1)
       Literal Float64_0.5
     Function quantile (children 2)
      ExpressionList (children 1)
       Identifier b
      ExpressionList (children 1)
       Literal Float64_0.9
    TablesInSelectQuery (children 1)
     TablesInSelectQueryElement (children 1)
      TableExpression (children 1)
       Subquery (children 1)
        SelectWithUnionQuery (children 1)
         ExpressionList (children 1)
          SelectQuery (children 3)
           ExpressionList (children 1)
            Function plus (alias b) (children 1)
             ExpressionList (children 2)
              Identifier x
              Literal UInt64_1
           TablesInSelectQuery (children 1)
            TablesInSelectQueryElement (children 1)
             TableExpression (children 1)
              Subquery (children 1)
               SelectWithUnionQuery (children 1)
                ExpressionList (children 1)
                 SelectQuery (children 2)
                  ExpressionList (children 2)
                   Function quantile (alias x) (children 2)
                    ExpressionList (children 1)
                     Identifier b
                    ExpressionList (children 1)
                     Literal Float64_0.5
                   Function quantile (children 2)
                    ExpressionList (children 1)
                     Identifier b
                    ExpressionList (children 1)
                     Literal Float64_0.9
                  TablesInSelectQuery (children 1)
                   TablesInSelectQueryElement (children 1)
                    TableExpression (children 1)
                     TableIdentifier fuse_tbl
           ExpressionList (children 1)
            Identifier x