Question

To where it bent in the undergrowth what does this line mean? the road not taken-robert frost

Answer 1

When he saw along the two roads in the forest, he was able to see up to some point ahead.  Beyond that, the road bent towards one side, as usually the paths in forest are curved.

So he tried to check the goodness and worthiness of the two paths.  That for checking if he could walk on that road or not.  An he could not see beyond a certain point.

Answer 2

Literally, then, to say that the road "bent in the undergrowth" means that, at a certain point, the speaker can no longer see which direction the road goes. The undergrowth obscures the road's direction from the speaker's sight. Moreover, and perhaps more importantly, he cannot see where it leads or where it ends.