Firstly, there are 3 main parts to a degreaser:
1.
Alkaline booster, to increase the pH, allowing the dirt, grease and grime to be effectively removed, for faster cleaning
2.
Solvent, to cut through tough grime and grease, as well as extract grime and grease from hard-to-get areas
3.
Surfactant, to hold grime and grease in the cleaning solution, preventing it from depositing back on the bikes surface once lifted off by the solvent and the alkaline solution
(there are also other components in professional degreasers, such as water softeners, hydro-tropes, anionic and ionic surfactants, specific application solvents, etc...)
The main source of the above 3 parts can be from using baking soda as a alkaline booster, methylated spirit as a solvent (I would use methylated spirit because it is water-soluble), and a small amount of dish-washing liquid as a surfactant.
An example formulation by volume would be:
- 50% Methylated Spirit
- 40% Water (H20)
- 5% Sodium Bicarbonate (Baking Soda)
- 5% Dish-washing Liquid
The methylated spirit and the sodium bicarbonate will work together to extract and lift the dirt/grime/grease, and the dish-washing liquid will work as a surfactant to stop it from depositing back on the bike again.
The dish washing liquid will also act as a wetting agent and a foam booster.
EDIT ----
Please also note, that the methylated spirit will prevent (or nearly prevent) any foam or the like from forming. If you want foam, you will have to substitute the methylated spirits with a mild solvent that is hydrophilic and not oil-based (lipophilic).
අනික අපි වගේ නෙමේ සෙන්ටිමීටර් දහයක් විතර වෙන්න ලං කරල අල්ලන්නෙ. මැජික් කෙමිකල් එකක් නෙමේ 
අනිවා අප්ඩේට් එකක් හම්බුනොත් දාන්නම්.
