The hierarchical layout already orders nodes depending on their connections (and the chosen layout orientation). However, forcing connected nodes onto the same layer (which is the technical term for a "level") is currently not easy. The simplest way is probably a two-pass approach:
Run the hierachic layout algorithm with option "Selected Elements Incrementally" and "Use Drawing As Sketch" on tab "General" disabled and option "Arrows define Edge Direction" on tab "Edge" enabled.
After the layout algorithm is finished manually adjust the positions of the same layer nodes. You only need to place those nodes roughly at the desired position.
Run the hierarchic layout algorithm once more, but this time with "Use Drawing As Sketch" enabled.