In 5e, is it at all possible to create half-subclasses?

Sonny is a great little game starred by a zombie who starts out with limited skills (a super-basic attack and a self-healing spell) and gains more skills as he levels up. At two points in the game, you get access to an additional skill tree (you can choose between five or so each time). Other than having more time to level up the skills from your first chosen tree (which is rendered moot by being able to respec at any point anyway), given two choices, the order in which you pick them has no bearing on what you can do once you’ve picked both.

I’m wondering whether this can be brought to 5e or it’s just too different from how 5e works to be compatible. I’m thinking a class could have five or six half-subclasses and the PC would be able to select one at level 3 and one at level 12 or so. Is this at all possible without leaving the PC with two weaker choices (the features they gain from level 12 to level 20 should be stronger than those they gain from level 3 to level 11)?