after install ubuntu budige 18.04 my second partition windows O.S not coming.
what should i do?
it directly goes to ubuntu budige.
press shift or press escape to display grub.
If you dont see windows in your grub list then that is I’m afraid a worry. You should check via a live CD that you haven’t accidentally erased that windows partition.
If you still have issues then run a boot repair https://help.ubuntu.com/community/Boot-Repair