I suggest to create a tag synonym analysis-and-odes $\to$ ca.classical-analysis-and-odes.
The tag analysis-and-odes has only five questions and empty tag info - so it does not seem to have any distinction from ca.classical-analysis-and-odes. Four of the five questions in this tag were asked by the same user, but since thy no longer have account on MathOverflow, we cannot even ask them whether their intention was to create something different from the existing top-level tag. For the list of questions, see here and here.
A reasonable alternative would probably be also to remove the tag manually, but a synonym solves the problem without bumping old question. And another advantage is that if somebody tries to create this tag in the future, it will automatically be change to the ca.classical-analysis-and-odes tag.