diff --git a/server/model/proc.go b/server/model/proc.go
index af81b4561b..6ed26d3170 100644
--- a/server/model/proc.go
+++ b/server/model/proc.go
@@ -71,17 +71,25 @@ func (p *Proc) IsParent() bool {
 // Tree creates a process tree from a flat process list.
 func Tree(procs []*Proc) ([]*Proc, error) {
 	var nodes []*Proc
-	for _, proc := range procs {
-		if proc.PPID == 0 {
-			nodes = append(nodes, proc)
-		} else {
-			parent, err := findNode(nodes, proc.PPID)
+
+	// init parent nodes
+	for i := range procs {
+		if procs[i].IsParent() {
+			nodes = append(nodes, procs[i])
+		}
+	}
+
+	// assign children to parrents
+	for i := range procs {
+		if !procs[i].IsParent() {
+			parent, err := findNode(nodes, procs[i].PPID)
 			if err != nil {
 				return nil, err
 			}
-			parent.Children = append(parent.Children, proc)
+			parent.Children = append(parent.Children, procs[i])
 		}
 	}
+
 	return nodes, nil
 }
 
diff --git a/server/model/proc_test.go b/server/model/proc_test.go
new file mode 100644
index 0000000000..5c876e4fd5
--- /dev/null
+++ b/server/model/proc_test.go
@@ -0,0 +1,69 @@
+// Copyright 2021 Woodpecker Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package model
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestTree(t *testing.T) {
+	procs := []*Proc{{
+		ID:      25,
+		PID:     2,
+		BuildID: 6,
+		PPID:    1,
+		PGID:    2,
+		Name:    "clone",
+		State:   StatusSuccess,
+		Error:   "0",
+	}, {
+		ID:      24,
+		BuildID: 6,
+		PID:     1,
+		PPID:    0,
+		PGID:    1,
+		Name:    "lint",
+		State:   StatusFailure,
+		Error:   "1",
+	}, {
+		ID:      26,
+		BuildID: 6,
+		PID:     3,
+		PPID:    1,
+		PGID:    3,
+		Name:    "lint",
+		State:   StatusFailure,
+		Error:   "1",
+	}}
+	procs, err := Tree(procs)
+	assert.NoError(t, err)
+	assert.Len(t, procs, 1)
+	assert.Len(t, procs[0].Children, 2)
+
+	procs = []*Proc{{
+		ID:      25,
+		PID:     2,
+		BuildID: 6,
+		PPID:    1,
+		PGID:    2,
+		Name:    "clone",
+		State:   StatusSuccess,
+		Error:   "0",
+	}}
+	_, err = Tree(procs)
+	assert.Error(t, err)
+}