func (ctx *DBCtx) CatTree(root bson.ObjectId) []Catergory {
all := []Catergory{}
var query *mgo.Query
if root.Valid() {
query = ctx.catColl.Find(bson.M{"ancestors": root})
} else {
query = ctx.catColl.Find(bson.M{"parent": bson.M{"$exists": false}})
}
query.All(&all)
return all
}
