Starting in Black and White, female Pokémon with Hidden Abilities have a 60% chance of passing on the Hidden Ability to their offspring when bred with a male Pokémon from the same Egg Group. In Generation VI, this was extended so that male and genderless Pokémon with a Hidden Ability can also pass it down if they are bred with Ditto. The chance of the offspring having either non-Hidden Ability is 20% each.
To get a Hidden Ability Treecko, you must either get an event Treecko, Grovyle, or Sceptile that already has its Hidden Ability or breed a Treecko, Grovyle, or Sceptile that has its hidden ability. Both ways require an event, and there aren't currently any events for a Hidden Ability Treecko, Grovyle, or Sceptile, so you'll have to trade in order to get one with its Hidden Ability. If you are breeding a Hidden Ability Treecko, Grovyle, or Sceptile and not getting a Hidden Ability Treecko, you just have bad luck.
There is a list of Pokemon that have Hidden Abilities and how you can get them here.
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