Start menu is one thing Microsoft has really focused on in Windows 10. It has been changed constantly in each preview build. You may remember in the last build, 9879, you can pull the edges of the Start menu to resize it in two directions. Now this ability is gone in build 9926. However, there is a Registry trick to bring that resizable Start menu  back.
This trick requires editing the Registry. So make sure you back it up before messing with it.
- Open the Run dialog. To do so, just press the Windows key + R on your keyboard. If you have a touchscreen monitor, you can choose to long tap (or long press) the Start button. Select “Run” from the menu as soon as you’re done.
- Type “regedit” (make sure to remove the quotes) and hit enter.
- On the left panel, navigate to HKEY_CURRENT_USER>Software>Microsoft>Windows>CurrentVersion>Explorer>Advance
- Then on the right side, right click/long tap the blank space then choose New -> DWORD (32-bit) Value.
- Enter the name: ” EnableXamlStartMenu” (remove the quotes).
That’s all. To apply the change, you need to log out then log in again.
via WinBeta