Delete nodes of tree data structure where children count is 0

[DebuggerDisplay("{Value}")]
public class TreeViewModel<TId, TValue> : IEnumerable<TreeViewModel<TId, TValue>>
{
    private readonly List<TreeViewModel<TId, TValue>> _children = new();
    public TreeViewModel(TId id, TValue value, TreeViewModel<TId, TValue> parent = null)
    {
        Id = id;
        Value = value;
        Parent = parent;
    }

    public TId Id;
    
    public TValue Value;
    
    public TreeViewModel<TId, TValue> Parent;

    public IReadOnlyList<TreeViewModel<TId, TValue>> Children => _children;

    public bool IsRoot => Parent is null;

    public bool IsLeaf => _children.Count == 0;

    public int Level => IsRoot ? 0 : Parent.Level + 1;
    
    public void AddChild(TId id, TValue value)
    {
        _children.Add(new TreeViewModel<TId, TValue>(id, value, this));
    }
    
    public void AddChild(TreeViewModel<TId, TValue> childTree)
    {
        childTree.Parent = this;
        _children.Add(childTree);
    }

    public void AddChildren(Dictionary<TId, TValue> children)
    {
        foreach (var child in children)
            AddChild(child.Key, child.Value);
    }

    public void RemoveChildren(Predicate<TreeViewModel<TId, TValue>> predicate)
    {
        _children.RemoveAll(predicate);
    }
    
    IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();

    public IEnumerator<TreeViewModel<TId, TValue>> GetEnumerator()
    {
        yield return this;

        foreach (var anyChild in Children.SelectMany(directChild => directChild))
        {
            yield return anyChild;
        }
    }
}

[DebuggerDisplay("{Value}")]
public class TreeViewModel<TId, TValue> : IEnumerable<TreeViewModel<TId, TValue>>
{
    private readonly List<TreeViewModel<TId, TValue>> _children = new();
    public TreeViewModel(TId id, TValue value, TreeViewModel<TId, TValue> parent = null)
    {
        Id = id;
        Value = value;
        Parent = parent;
    }

    public TId Id;
    
    public TValue Value;
    
    public TreeViewModel<TId, TValue> Parent;

    public IReadOnlyList<TreeViewModel<TId, TValue>> Children => _children;

    public bool IsRoot => Parent is null;

    public bool IsLeaf => _children.Count == 0;

    public int Level => IsRoot ? 0 : Parent.Level + 1;
    
    public void AddChild(TId id, TValue value)
    {
        _children.Add(new TreeViewModel<TId, TValue>(id, value, this));
    }
    
    public void AddChild(TreeViewModel<TId, TValue> childTree)
    {
        childTree.Parent = this;
        _children.Add(childTree);
    }

    public void AddChildren(Dictionary<TId, TValue> children)
    {
        foreach (var child in children)
            AddChild(child.Key, child.Value);
    }

    public void RemoveChildren(Predicate<TreeViewModel<TId, TValue>> predicate)
    {
        _children.RemoveAll(predicate);
    }
    
    IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();

    public IEnumerator<TreeViewModel<TId, TValue>> GetEnumerator()
    {
        yield return this;

        foreach (var anyChild in Children.SelectMany(directChild => directChild))
        {
            yield return anyChild;
        }
    }
}