Here is an example of Python code that generates a process tree for a hypothetical Purchase-to-Pay process using pm4py:
```python
from pm4py.objects.process_tree.obj import ProcessTree, Operator

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

# Create the process tree for the Purchase-to-Pay process
# Step 1: Purchase Request
purchase_request = ProcessTree(label="Purchase Request", parent=root)

# Step 2: Purchase Order
purchase_order = ProcessTree(label="Purchase Order", parent=root)

# Step 3: Goods Receipt
goods_receipt = ProcessTree(label="Goods Receipt", parent=root)

# Step 4: Invoice Receipt
invoice_receipt = ProcessTree(label="Invoice Receipt", parent=root)

# Step 5: Payment
payment = ProcessTree(label="Payment", parent=root)

# Create a SEQUENCE for the Purchase Order to Invoice Receipt flow
purchase_order_to_invoice_receipt = ProcessTree(operator=Operator.SEQUENCE, parent=root)
purchase_order_to_invoice_receipt.children.append(purchase_order)
purchase_order_to_invoice_receipt.children.append(goods_receipt)
purchase_order_to_invoice_receipt.children.append(invoice_receipt)

# Create a SEQUENCE for the Payment flow
payment_flow = ProcessTree(operator=Operator.SEQUENCE, parent=root)
payment_flow.children.append(payment)

# Add the children to the root node
root.children.append(purchase_request)
root.children.append(purchase_order_to_invoice_receipt)
root.children.append(payment_flow)

# Set the parent of each child node
purchase_request.parent = root
purchase_order.parent = purchase_order_to_invoice_receipt
goods_receipt.parent = purchase_order_to_invoice_receipt
invoice_receipt.parent = purchase_order_to_invoice_receipt
payment.parent = payment_flow

print(root)
```
This code generates a process tree for a hypothetical Purchase-to-Pay process with the following structure:
```
PARALLEL
|
|-- Purchase Request
|-- SEQUENCE
|    |
|    |-- Purchase Order
|    |-- Goods Receipt
|    |-- Invoice Receipt
|-- SEQUENCE
|    |
|    |-- Payment
```
Note that this is just one possible representation of a Purchase-to-Pay process, and you may need to modify the code to fit your specific use case.