Here's a Python code snippet that creates a process tree for a hypothetical Purchase-to-Pay process using the `pm4py` library. This process tree includes activities like 'Create Purchase Order', 'Receive Goods', 'Create Invoice', 'Pay Invoice', and 'Archive Invoice'. It also includes silent steps (tau) for waiting periods.

```python
from pm4py.objects.process_tree.obj import ProcessTree, Operator

# Create root node
root = ProcessTree(operator=Operator.PARALLEL)

# Create child nodes
create_po = ProcessTree(label="Create Purchase Order", parent=root)
wait_goods = ProcessTree(label="tau (Wait for Goods)", parent=root)
receive_goods = ProcessTree(label="Receive Goods", parent=wait_goods)
create_invoice = ProcessTree(label="Create Invoice", parent=receive_goods)
wait_payment = ProcessTree(label="tau (Wait for Payment)", parent=create_invoice)
pay_invoice = ProcessTree(label="Pay Invoice", parent=wait_payment)
archive_invoice = ProcessTree(label="Archive Invoice", parent=pay_invoice)

# Set parent for root's children
root.children.append(create_po)
root.children.append(wait_goods)

# Set parent for wait_goods' children
wait_goods.children.append(receive_goods)
wait_goods.children.append(create_invoice)

# Set parent for create_invoice's children
create_invoice.children.append(wait_payment)
wait_payment.children.append(pay_invoice)

# Set parent for pay_invoice's child
pay_invoice.children.append(archive_invoice)

print(root)
```

This code creates a process tree where 'Create Purchase Order' and 'Wait for Goods' (which includes 'Receive Goods' and 'Create Invoice') are executed in true concurrency. After 'Create Invoice', the process waits for payment, then pays the invoice, and finally archives the invoice.