No superflat preset text option to generate woodland mansions

When in the presets section text box of creating a superflat world, there is no text to spawn woodland mansions or not. for example: preset superflat world in a roofed forest biome.

3;minecraft:bedrock,2*minecraft:dirt,minecraft:grass;29;mansion

29 being the roofed forest biome id.

but when I type mansion or woodlandmansion at the end and create the world, no mansions spawned, i even tried to locate one with /locate. nothing.