hieght of complete binary tree=$\left \lceil log _{2}n \right \rceil$
=$\left \lceil log _{2}63 \right \rceil$
=$\left \lceil 5.9 \right \rceil$
=6
Alternative
max number of nodes = $2^{(h+1)}-1$ put value $h=6$
= $2^{6}-1$
=$63$ number of node given in complete binart tree