Ubuntu 20.04 dual boot with windows 10, not showing grub menu, directly boot into Ubuntu

i had 4 partitions on my hdd, C, D and 2 reserved, i had gpt style, now to install ubuntu i shrink D from 338 to 278 GB, start installing ubuntu on remaining approx 60 GB, from which i used 59.7 GB for installation and other for Reserve boot bios type what it wants to install grub, all installation goes successful but now its directly booting into ubuntu 20.04 not showing grub menu to make selection between installed OSes. please help how i can have it working? regards

Edit your /etc/default/grub as such.
Edit or replace these lines;
GRUB_DEFAULT=0
#GRUB_DEFAULT=saved
#GRUB_SAVEDEFAULT=true
#GRUB_TIMEOUT_STYLE=hidden
GRUB_TIMEOUT_STYLE=menu
GRUB_TIMEOUT=10

Commit the changes then don't forget to... sudo update-grub then reboot.