Hi Smita, this is because of the setting of dwtmode. If you want to see the behavior you expect above, then do
before computing the wavelet transform.
x = randn(1e3,1);
[C,L] = wavedec(x,3,'sym4');
If you look at the L output, you will see the number of coefficients in the signal, L(end), and then 500 coefficients at level 1, 250 at level 2, etc.
Now return dwtmode to the default setting and repeat
[C,L] = wavedec(x,4,'sym4');
Now you see the number as you report above.