I have a multi-sample vcf file of 350 loci spread across the genome from 85 individuals. I want to use this to ultimately build phylogenetic trees. For this i want to first make fasta sequences of 100kb length for each of the 350 loci for the 85 individuals, something similar to what GATK FastaAlternateRefrenceMaker does. I don't know how to specify sequence length in this tool though. Is it even possible to do what I am trying to do using this tool or any other tool? I would like some suggestions on how to take care of this.