To add an account, I click on a button below the treeview.

To remove an account, I click on a trash image in the treeview.

I think it doesn't look consistent. Here are two possibilities I see:

 + remove the trash images, and add a remove button below the treeview
 + add a special item in the treeview "Add account". When selected, it would do what we can see when clicking the add button right now.

I think the second solution might be the best, because I don't think it's really nice to change the content of the dialog when the user clicks on a button (it's confusing).