code: public CompoundTag add(Tag ch) {
          subElements.put(ch.getName(), ch);
          long sz = getSize() + ch.totalSize();
          byte length = 1;
          long v = (sz + 1) >> BIT_IN_BYTE;
          while (v > 0) {
              length++;
              v = v >> BIT_IN_BYTE;
          }
          size = new VINT(0L, length, sz);
          return this;
      }
docs: method to add child tag to this {@link CompoundTag}, updates the size on add
  
  @param ch
  - child {@link Tag} to be added
  @return - this for chaining