Dual boot Ubuntu with Windows on Acer Aspire

@oldfred thanks very much for your support, links you shared really help me out. Following are the steps of the solution that works for me.

Press F2 to enter into BIOS and do following:

• Set supervisor password from Security menu option.

• Set BootMode to 'UEFI' from Boot menu option.

• Enable SecureBoot from Boot menu option.

• From Security menu option - Select 'UEFI file as trusted for
  executing' press Enter then 'HDD0' appears press Enter then 'EFI'
  appears press Enter then select 'ubuntu' option from the list (only
  listed if you have ubuntu installed already) press Enter then choose 'shimx64.efi' (In my case it's the third entry) press Enter give it a name and press Enter.

• Go back to Boot menu option and under Boot priority goto
  'ubuntu' item in the list and press F6 until it become top most item in the list. Repeat same for 'Windows Boot manager' until it becomes second top most item in the list.

• Press F10 to save changes and exit.