Query to seed many to many table
If you're using SQL Server, You can use CROSS APPLY to return 1 Branch row for each Employee row:

SELECT e.ID AS EmployeeID,
  e.Name AS EmployeeName,
  b.BranchID,
  b.BranchName
FROM Employee e
CROSS APPLY (SELECT ID AS BranchID, BranchName FROM Branch) b
ORDER BY EmployeeID


See working db&lt;>fiddle.

For Postgres, similar query but using LEFT JOIN LATERAL instead:

SELECT e.ID AS EmployeeID,
  e.Name AS EmployeeName,
  b.ID AS BranchID,
  b.BranchName
FROM Employee e
LEFT JOIN LATERAL (SELECT ID, BranchName FROM Branch) b ON true
ORDER BY EmployeeID


Working db&lt;>fiddle here.