Thanks for your kind guidance… Much appreciated!!!.
I was also installing ubuntu 18.04 for the first time along with my windows environment. Have tried the option " Something else" and had already created separate partitions for this installation, but got stuck with some issues (e.g No root was defined etc). I tried with other Options, this time " Use LVM with the new ubuntu installation" . But unfortunately this one click caused loss of my windows environment (around 600 GB data, with more than 100 applications configurations/installations ). No doubt its my mistake, but just a humble request if these options can be proceeded with warning dialog box and clearly defining the operations sections in future.
Thanks…