API: get all benefits under tiers

I can’t find my way with API. I am making a call to get campaign and I get benefits and tiers in that campaign. But they are in no way linked, I mean I can’t get them so I know which benefits are under which tier. I make a call like:

campaigns/{$campaign_id}?include=benefits,tiers&fields".urlencode("[tier]")."=title,description&fields".urlencode("[benefit]")."=title,description

I get result like:

[benefits] => [list of benefits]
[tiers] => [list of tiers]

and no idea which benefit is under which tier. I need result to be like:

[tiers] =>
[tier1] => title, description, [list of benefits] => benefit title, benefit description
[tier2] => title, description, [list of benefits] => benefit title, benefit description

But can’t find how to do that. Any help ?