Notes on appearing Held Items on the Battle Tree:

Datamine: https://docs.google.com/spreadsheets/d/1D7T0jCHBkDppjTB0_rJyK0houk8zE3wLmZ1DlVXEkXg/edit#gid=0

Items:

Note: All Mega Stones and Z-Crystals appear in the Battle Tree.

Type-hit Boosters:

1. Absorb Bulb
2. Cell Battery 
3. Luminous Moss 
4. Snowball

Choice Items:

1. Choice Band
2. Choice Scarf
3. Choice Specs

Other consumables:

1. Air Balloon
2. Eject Button
3. Red Card
4. Weakness Policy

 Berries:

1. Apicot Berry 
2. Babiri Berry 
3. Charti Berry
4. Cheri Berry
5. Chesto Berry
6. Chople Berry
7. Coba Berry
8. Colbur Berry
9. Custap Berry
10. Enigma Berry
11. Ganlon Berry
12. Haban Berry
13. Jaboca Berry
14. Kasib Berry
15. Kebia Berry
16. Kee Berry
17. Liechi Berry
18. Lum Berry
19. Maranga Berry
20. Occa Berry
21. Passho Berry
22. Payapa Berry
23. Persim Berry
24. Petaya Berry
25. Rawst Berry
26. Rindo Berry
27. Roseli Berry
28. Salac Berry
29. Shuca Berry
30. Sitrus Berry
31. Tanga Berry
32. Wacan Berry
33. Yache Berry

Focus Items:

1. Focus Band
2. Focus Sash

Herbs:

1. Mental Herb 
2. Power Herb
3. White Herb

Incense:

1. Lax Incense 
2. Sea Incense

Permanent Held Items:

1. Assault Vest 
2. Big Root
3. Binding Band
4. Bright Powder 
5. Eviolite
6. Expert Belt
7. Float Stone
8. Iron Ball
9. King's Rock
10. Life Orb
11. Muscle Band
12. Quick Claw
13. Razor Claw
14. Razor Fang
15. Rocky Helmet
16. Safety Goggles
17. Scope Lens
18. Shell Bell
19. Thick Club
20. Wide Lens
21. Wise Glasses
22. Zoom Lens

Type-enchancers.

1. Black Belt
2. Black Glasses 
3. Charcoal
4. Dragon Fang
5. Hard Stone
6. Magnet
7. Miracle Seed
8. Mystic Water
9. Never-Melt Ice
10. Sharp Beak
11. Silk Scarf
12. Soft Sand
13. Spell Tag
14. Twisted Spoon

Terrain Seeds:

1. Electric Seed 
2. Misty Seed
3. Psychic Seed

 Recovery Items:

1. Black Sludge 
2. Leftovers

Status Orbs:

1. Flame Orb 
2. Toxic Orb

Duration Increasers:

1. Damp Rock
2. Heat Rock
3. Icy Rock
4. Light Clay 
5. Smooth Rock
6. Terrain Extender

Items that Don't Appear:

Terrain Seeds:

1. Grassy Seed 

Duration Extenders:

1. Grip Claw 

Type-enhancers:

1. Metal Coat
2. Poison Barb
3. Silver Powder 
4. (Soul Dew) (Recently made legal, but doesn't appear in-game)

Permanent Held Items:

1. Amulet Coin
2. Lagging Tail
3. Metronome
4. Ring Target
5. Shed Shell
6. Sticky Barb
7. Smoke Ball

 Other Consumables:

1. Adrenaline Orb