Bottlebrushes are an emerging class of polymers, characterized by a high density of side chains grafted to a linear backbone that offer promise in creating materials with unusual combinations of mechanical, chemical, and optoelectronic properties. Understanding the role of molecular architecture in the organization and assembly of bottlebrushes is of fundamental importance in polymer physics, but also enabling in applications. Here, we apply field-theoretic simulations to study the effect of grafting density, backbone length, and side-chain (SC) length on the structure and thermodynamics of bottlebrush homopolymer melts. Our results provide evidence for a phase transition from an isotropic to a nematic state with increasing grafting density and side-chain length. Variation in the backbone length is also observed to influence the location of the transition, primarily for short polymers just above the star to bottlebrush transition.