Encapsulates the process of inserting a frond uw into the left side frond group.

def __insert_frond_LF(d_w, d_u, dfs_data):
    """Encapsulates the process of inserting a frond uw into the left side frond group."""
    # --Add the frond to the left side
    dfs_data['LF'].append( (d_w, d_u) )
    dfs_data['FG']['l'] += 1

    dfs_data['last_inserted_side'] = 'LF'