how to recursive query items?

i have items with children, the parent and children are M2M same types, as below:

```
func (Item) Fields() []ent.Field {
return []ent.Field{
field.String("code").
NotEmpty().
StructTag(`validate:"required,max=128"`),
field.String("name").
NotEmpty().
StructTag(`validate:"required,max=128"`),
field.Int("level").
Default(1).
StructTag(`validate:"required,gte=0"`),
field.String("parent_id").
Optional(),
}
}

func (Item) Edges() []ent.Edge {
return []ent.Edge{
edge.To("children", Item.Type).
From("parent").
Unique().
Field("parent_id"),
}
}
```

i try a query by:

```
func itemQuery(q *ent.ItemQuery) {
ctx := context.Background()
count, err := q.QueryChildren().Count(ctx)

if count > 0 {
q.WithChildren(itemQuery)
}
}

...

WithItems(itemQuery)
```

but it cannot work, so how to query items with all theire children? untill the leaf node?