I would remove the Bonsai Tree. Replace it with a larger driftwood of some sort.
PBs (alone in that tank) and at that size easily spook with minimal surrounding movement. Being spooked, instict tells them to find somewhere to hide.
And that Bonsai Tree doesn't help.
Dimmer lights or room lighting would calm it down.
Another "to feed" way is that to get some larger Tiger Barbs as dithers and a "teacher fish" for your PB to start trying pellets. Thats what I did for all juvie PBs i grow out to eventually go on a strict pellet diet.
This method is only temporary. Tiger Barbs need to be rehomed once PB readily eats pellet.