John Gill Commentary 1 Kings 6:31

"And for the entrance of the oracle he made doors of olive-wood: the lintel [and] door-posts were a fifth part [of the wall]." — 1 Kings 6:31 (ASV)

And for the entering of the oracle he made doors [of] olive
tree
The door of the holy of holies was a two leaved or folding door, made of olive wood; typical of Christ, the door into the church above and below, the way to heaven and eternal life, the true olive tree:

the lintel [and] side posts [were] a fifth part [of the wall] ;
four cubits, twenty cubits being the breadth of the oracle; or the lintel was four cubits, twenty being the height of it also, (1 Kings 6:20) .