I have a project which have completed the basic models(at master), then I commit them.

Then I create two branchs user and product using:

git checkout -b user
git checkout -b product
git checkout user

Then I add the codes in the user branch, but I found that I have to make some changes for the basic models.

Then I switch to master:

git checkout master

But I found that the modification I made in the user branch is visible in the working directory now.

How to avoid this? Since the change to master and modification will be frequency.