boot - GRUB not detecting Legacy BIOS windows 10 installation even with legacy BIOS Ubuntu 16.04LTS installation - Ask Ubuntu

ok might seem common problem couldn't find answers anywhere specific case. freed , created unallocated space c:\ drive in windows , went well. while installing ubuntu 16.04lts, popup came up(sorry not allowed embed images yet.): popup.jpg

it means windows installed in bios mode, , didn't want force install ubuntu in uefi clicking "continue in uefi", clicked "go back" instead. installation loaded while , automatically moved forward next step, assumed it'll continue installation in bios mode, detected freedos(my laptop shippped it, on /dev/sda1), , not windows 10(which on /dev/sda2), , gave me option "install ubuntu alongside freedos" only, not windows10. unfortunately considered grub detect later , chose "something else", created / , swap unallocated space, , installed ubuntu. after installing grub isn't detecting windows 10.

i confirmed ubuntu installation legacy bios there's no /sys/firmware/efi directory, shouldn't bios vs uefi problem, also, bios has "legacy support" enabled. also, os-prober shows freedos, below:

/dev/sda1:freedos:freedos:chain tried boot-repair , performed "recommended repairs", nothing changed. tried running startup repair inside windows 10 setup bootable usb, couldn't fix it. i've got no idea how working, there missing? appreciated !

edit: ok, tried adding custom menu entry 40_custom in /etc/grub.d/ below:

menuentry 'windows 10' { set root='(hd0,msdos2)'  //as windows on /dev/sda2 chainloader +1 } 

but still, sudo update-grub2 shows:

generating grub configuration file ... found linux image: /boot/vmlinuz-4.4.0-45-generic found initrd image: /boot/initrd.img-4.4.0-45-generic found linux image: /boot/vmlinuz-4.4.0-31-generic found initrd image: /boot/initrd.img-4.4.0-31-generic found freedos on /dev/sda1 done 

no windows :(

ok, solved problem using easybcd windows 10. 1 should prefer using gnu grub2 default bootloader, more last resort solution.

note: if anyone's having same problem, first read , try things did (given in question), , comments, if nothing works out.

as said in question comments, had override grub2 windows bootloader boot in windows 10. once booted, 1 can install easybcd , run it. follow this guide add entry ubuntu in windows boot menu. on rebooting, boot menu show both ubuntu , windows installations, there's catch. on selecting windows, system proceeds usual windows boot, when ubuntu selected, windows bootloader first call grub2, wherein can boot ubuntu(aka "chainloading").

there's surely drawback 1 has go through 2 boot menus boot ubuntu now, hence i'll again, ad hoc solution , 1 should prefer trying other solutions first.