code: func (p *Pod) GetAppsTreeStoreIDs() ([]string, error) {
  	var treeStoreIDs []string
  	apps, err := p.getApps()
  	if err != nil {
  		return nil, err
  	}
  	for _, a := range apps {
  		id, err := p.GetAppTreeStoreID(a.Name)
  		if err != nil {
  			return nil, err
  		}
  		if id != "" {
  			treeStoreIDs = append(treeStoreIDs, id)
  		}
  	}
  	return treeStoreIDs, nil
  }
docs: // GetAppsTreeStoreIDs returns the treeStoreIDs of the apps images used in
  // this pod.
  // TODO(yifan): Maybe make this unexported.