get commit ID from a tree object ID

Hello,

let's say I have made an annotated tag on a certain treeish:

$ git tag -a -m msg tagname HEAD:

Now, I can try to see the content of the tag:

$ git tag -v tagname object 42a1c36553a50ceae2f75ffc4b1446c6c393eae7 type tree tag tagname tagger clime <clime@redhat.com> 1521288727 +0100

msg error: no signature found

Can I use that object ID 42a1c36553a50ceae2f75ffc4b1446c6c393eae7 to get back to a particular commit from which the tag was created? The reason is that I would eventually like to checkout that commit.

Thank you clime