Boot option missing in Windows Boot Manager after installing live Ubuntu on hard disk with UNetbootin

Question

I am a complete newbie to Ubuntu so I am not sure what the correct terminology for this is. Anyway, here's what I did:

1. Downloaded ubuntu-18.04.2-desktop-amd64.iso and unetbootin-windows-661.exe from their respective official sources.
2. Fired up unetbootin-windows-661.exe.
3. Selected "Ubuntu" from the "==Select Distribution==" drop down menu.
4. Browsed to the ISO disk image that I had downloaded.
5. Selected "Hard disk" from the type menu in the bottom left corner.
6. Pressed OK.

Then I let the setup do it's thing and after it was done the message said that I would see an option named "UNetbootin" in the bootup screen the next time I reboot. So I rebooted but there was no such option! On the black screen titled "Windows Boot Manager" the only two options were Windows 7 and Macrium Reflect Recovery which I installed for backup purposes.

I tried rebooting multiple times but there's still no option to boot into Ubuntu. I also tried installing the live Ubuntu again and again. The setup terminated successfully every time and told me the same thing but there's still no option to boot into Ubuntu in the boot screen. I would boot using a usb drive but I don't have one to spare at the moment so please help me!

Concerning @Akib Azmain's answer, here's what happened:
I followed the listed steps and created a boot entry for the C:\ partition and this time there was a boot entry in the boot menu. However, it led me to this. Being a complete newbie to Ubuntu, I had no idea what to make of it. So I went back and created boot entries for all four partitions on my disk. All of them ended the same way.

I haven't tried the second option yet. I will do after I finish writing this.

Answer 1

Looks like your problem is that GRUB2 is properly configured correctly. To solve your problem you have to do the following:

1. Install EasyBCD.
2. Open EasyBCD.
3. In the left menu (EasyBCD Toolbox) select "Add New Entry".
4. In the right of EasyBCD Toolbox select "Linux/BSD" under "Operating Systems".
5. As Ubuntu 18.04.2 uses GRUB2 so select "GRUB 2" in the "Type" dropdown menu.
6. In the "Name" field give the name of the entry you want. (Eg. Ubuntu, Ubuntu Linux, Ubuntu 18.04.2)
7. In the "Drive" field select the partition you used to install Ubuntu. The option should contain "Partition [the number of partition] (Linux - [the size of the partition])".
8. Click the + to add the entry.

Now try to boot Ubuntu with that entry. If it fails then:

1. Create a folder named "boot" in the root directory any NTFS partition.
2. Create a folder named "grub" inside that directory.
3. Create a file named "grub.cfg" inside the "grub" directory.
4. Write the following in the file.

source (hd0,1)/boot/grub/grub.cfg

5. Boot with that entry.
6. If you fail to boot Ubuntu then open that file and replace 1 with 2, 3, 4... until you are able to boot Ubuntu.

After booting Ubuntu, you can reconfigure the GRUB by executing the following commands:

sudo su
grub-install /dev/sda
update-grub