Presentation__c presentation = new Presentation__c(Name = '100test');
insert presentation;
Integer sequencesCount = 100;
List<Sequence__c> sequences = new List<Sequence__c>();
for (Integer i = 0; i < sequencesCount; ++i) {
    sequences.add(new Sequence__c(Name = '100test' + i));
}
insert sequences;
List<SequenceFile__c> sequenceFiles = new List<SequenceFile__c>();
for (Integer i = 0; i < sequencesCount; ++i) {
    sequenceFiles.add(new SequenceFile__c(Name = sequences[i].Name,Sequence__c = sequences[i].Id, Status__c = 'Active'));
}
insert sequenceFiles;