[ابو بيشو]

Nothing is more ugly than a street without trees. Is it grammatically correct to say "more ugly"?
.................................................. .................................................. .............
Yes, this is grammatical. Many two-syllable adjectives can form the comparative and superlative with either -er, -est or with more, most. In fact, the comparative/superlative with more, most is becoming more common.
See Comparatives and superlatives in the Archives for more.