Icon for selecting related data [on hold]

I am working on a web application that includes a feature to export some data.

When exporting this data, there are 2 types of entities that the user can select: Type A and Type B. Type A is its own thing, but owns 1 or more instances of Type B. Sometimes the user wants to export some instances of Type A, sometimes they will want to export some instances of Type B, and sometimes they want to export both at the same time.

To present the data to the user, I'm using a dialog with the following layout:

So now to the actual question:
Since Type A owns one or more instances of Type B, I'd like to have an icon in the row for a Type A to quickly select all entries of Type B owned by that Type A, but I'm having a hard time coming up with an icon that is clear.

Right now, I use this icon: with an instant tool-tip that basically says "Select all Type B for this Type A".

I know I should probably just do some user testing to see if this is clear enough, but is there a "standard" icon commonly used for this scenario? Is the arrow icon I've chosen sensible?