I have installed Windows 10 in My Dell Inspiron 620s.
When installation of the Ubuntu 16.04.1 64-bit is installed(first time) and when I restarted the system after the fresh installation of Ubuntu alongside with Windows 10.
It started the system in Windows itself without any selection screen of the O.S.
Note: My system's BIOS mode is Legacy(don't know it will be handy or not.)