The Champoline (mushroom) is unlocked early on in the game when you obtain the first ability. You need to build a tower of them (10 stacked) to unlock the achievement. This can be done near the beginning but it is easier once you have more abilities collected.
Go to an area with some open space, select the mushroom shape on BUD's backpack using
/
or hold
, then select it from that overlay. Plant one by pressing
, then jump up on it and plant another on top. Make sure to grab onto the mushroom when landing from a jump to avoid falling off. Once you have stacked 10, the achievement should unlock (if not, stack a few more).