A   B
1 a   x
2 a   y
3 a   z
4 b   i
5 b   h
6 b   w

A   B   C   D
1 a   x   y   z
2 b   i   h   w

={UNIQUE(FILTER(A1:A, A1:A<>"")),
  ARRAYFORMULA(SPLIT(TRANSPOSE(
  QUERY(TRANSPOSE(IF(TRANSPOSE(
  QUERY(TRANSPOSE(
  QUERY({A1:B}, "select count(Col1)
                 where Col1 !=''
                 group by Col1
                 pivot Col2", 0)),
                "select Col2, Col3", 0))>=1,
  QUERY({A1:B}, "select count(Col1)
                 where Col1 !=''
                 group by Col1
                 pivot Col2
                 limit 0"), ))&"♥", ,
  COLUMNS(IF(TRANSPOSE(
  QUERY(TRANSPOSE(
  QUERY({A1:B}, "select count(Col1)
                 where Col1 !=''
                 group by Col1
                 pivot Col2", 0)),
                "select Col2, Col3", 0))>=1,
  QUERY({A1:B}, "select count(Col1)
                 where Col1 !=''
                 group by Col1
                 pivot Col2
                 limit 0"), )))), "♥ "))}