Line coding for a modulation order that is not power of 2 In case a symbol encodes a non-integer number of bits, how is done the bit-symbol pairing?

For example, we have a 3-levels FSK with bit rate of 1Mbps and a sequence 01011001. What is the symbol period? What is the sequence of symbols?

Note: My guess is that the actual bit period and symbol period are the same. Hence, the use of 3-levels only helps to increase somehow the robustness of the error detection (similar to Hamming coding or 8b/10b encoding). Thus, we apply a bipolar AMI (Alternate Mark Inversion) to the bit sequence to obtain {0,+1,0,-1,+1,0,0,-1}. Finally, in the receiver, we demodulate every symbol 0 as a bit 0, and every symbol +1 and -1 as a bit 1.
Another reason to encode to $3$ level is that the occupied bandwidth is less.   This is often driven by an emission mask constraint  for transmitter certification. To satisfy this constraint,  the tradeoff is made on symbol distance.   It is however a costly tradeoff affecting receiver sensitivity because the multi level scheme is done post detection where every factor of $2$ increase in throughput costs $6$ dB in sensitivity.   Other schemes like QAM cost only $3$ dB in sensitivity when doubling the number of bits per signaling element.  With the multilevel FSK, you do however retain some of the advantages of an FM strategy in  terms of the CIR performance of the system.