We can do this by using the Tracing Mode on the Product Tree. Here are the steps
1. On successfully logging in, go to Product Tree.
2.  From the product tree, select the required item, for e.g.,Requirement.
3.  Click “Tracing Mode” from the product tree toolbar.
4.  This opens another product tree on the right side of the screen.
5. In the right-side product tree, select the “Toggle Checkbox mode” which shows the chckbox for every work item
6. select the multiple item (test cases) to link to by checking the checkbox.
7. Click “Create Tracing” icon to complete the tracing.