How to make ubuntu show on boot menu options

I have installed ubuntu 18.04 in my pc which came pre-installed with windows 10. I am now in "try ubuntu without install" and the detail of my partitions is as below:

ubuntu@ubuntu:~$ sudo parted -l
Model: ATA ST1000LM035-1RK1 (scsi)
Disk /dev/sda: 1000GB
Sector size (logical/physical): 512B/4096B
Partition Table: gpt
Disk Flags: 

Number  Start   End     Size    File system  Name                          Flags
 1      1049kB  274MB   273MB   fat32        EFI system partition          boot, hidden, esp
 2      274MB   290MB   16.8MB               Microsoft reserved partition  msftres
 3      290MB   506GB   506GB   ntfs         Basic data partition          msftdata
 4      506GB   685GB   178GB   ntfs         Basic data partition          msftdata
 6      685GB   899GB   215GB   ext4
 5      999GB   1000GB  1049MB  ntfs         Basic data partition          hidden, diag


Model: SanDisk Cruzer Blade (scsi)
Disk /dev/sdc: 7799MB
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Disk Flags: 

Number  Start   End     Size    File system  Name                  Flags
 1      1049kB  7799MB  7798MB  fat32        Microsoft Basic Data  msftdata

How shold i proceed from here, currently i can only see ubuntu when i have my flash drive connected. I can smoothly log in to windows in the 'windows bootmgr' option in the boot menu. i have already installed ubuntu. My ubuntu is installed in partition number 6. 215GGB.