Complex sentence: Tchaikovsky wrote a symphonic poem, "Fatum", after he had finished his First Symphony and first opera, "The Voyevoda", in which he dabbled with the free form the new genre offered.
Split into simpler sentences: Tchaikovsky wrote a symphonic poem, "Fatum", after he had finished his First Symphony and first opera, "The Voyevoda". There, he dabbled with the free form the new genre offered.