Once per turn, you can use your a bonus action to bite (use 1 charge) to Heal = 3d4 + Consitution modifier + 1.5*PC lv (round down)

+ Gluttony: you can eat all the core and seed of the apple to use all 4 charges at once and heal 1 hit die every hour (this effect lasts for 24h).
Once the healing effects end, a small apple tree grows out of your stomach make you feel exhausted lv 5 in the next 72h (It will disappear spontaneously).
The exhaustion can only be leveled down 1 per time by using Greater Restoration spell or Long rest or Potion of Vitality (max 2 level/day).

Notes: Timesless apple - Require attunement, Buff