note head direction not automatically rearranged for two adjacent pitches when two voices are used instead of a chord

[Soo Lee]

\new Staff
<<
\new Voice = "first"
  { \voiceOne g'4 }
\new Voice= "second"
  { \voiceTwo \stemUp f'4 }
>>

This example shows G and F note heads are drawn in an overlapping way. I did not want to use a chord but wanted them to be merged to look like a chord. Is there an option to do this?

Thank you!

Best,

Soo