Well, try this:
using an example from the docs:
load fisheriris;
t = classregtree(meas,species,...
'names',{'SL' 'SW' 'PL' 'PW'})
I was able to get the property-inspector:
tr=view(t)
inspect(tr)
..what didnt help a lot...
Now I took the handles of all children of tr, that are text-elements:
allHandles=findall(tr,'Type','text')
Next, I just changed the FontSize:
set(allHandles,'FontSize',16)
and there you go :) it is working!
To see and edit other properties, you could now use the inspect-method, as I was doing at my first try, but with the text-handles of course. normally, there should be all other properties available as for normal text-elements. Just check the docs for uicontrol + text.