Show Git subtree commit history when --squash option was used

Question

Is there any way to show only subtree history, like with git log but filtering only specific subtree's related commits?

When I add a subtree with --squash option only a merge commit is shown, but the subtree history is still somewhere, since I can split and push it as standalone repository with its complete history.

How can I see that apparently hidden history when --squash option is used?